996 Rear screen leak - all 'normal' routes tried, help required please!!

t911r · 23 Mar 2025

Hi all,

I have a 1998 996 coupe with a sunroof, I have water ingress into the rear of the car via the LHS (passenger) side near the drain tube clip.

Before I start I want to be clear that I've searched the forum(s) high and low for this particular issue with no luck.

I have already:

Last week, had the rear screen glass out, cleaned and rebonded professionally with new OEM rear rubber outer seal and inner sealing frame.
Has the drains of the sunroof off, blown through and reconnected
Had the plastic clips which attach the sunroof 'cassette' to the rear drain pipes taken off and re-sealed
Checked the sunroof drain pipes are not cracked or leaking
Checked the rear roof rack mounting points/cover/bolt is not leaking.

My issue is of water running down the first third of the inside of the body next to the rear screen glass, hitting the 2nd 'clip' that holds the LHS sunroof drain tube (passenger) in place and dripping onto everything.

Over a few hours it can result in a fairly large amount of water and it seems to have been happening for years judging by the state of the carpet and seats when I removed them.

Tried my best to capture the issue in the below images.

Any thoughts or theories I can chase are appreciated greatly.

911UK · 23 Mar 2025

you do have checked the usual places

t911r · 8 Apr 2025

Update, see attached photos, I can replicate what I believe to be the entry point but I can't quite pinpoint where it's getting in! Any help appreciated.

WilmslowSi · 8 Apr 2025

I had/have a similar issue to you. I'd identified that the plastic connectors that join the rear drain tubes to the corners of the sunroof cassette were letting water run past them, so unclipped them and replaced the perished sealant, thinking I'd cured the issue. It was much better, but I still got a damp headlining in the rear corners but only after really heavy rain... took a lot if investigating with hosepipe and phone camera to record the leak and I found it was coming from the same place yours appears to be; the top corner seals of the rear windscreen. I did this;

t911r · 8 Apr 2025

Thank you so much, sadly I have done this (took ages and twice lol!) but it seems to be something else still now that's resolved, appreciate your help though!

WilmslowSi said:
I had/have a similar issue to you. I'd identified that the plastic connectors that join the rear drain tubes to the corners of the sunroof cassette were letting water run past them, so unclipped them and replaced the perished sealant, thinking I'd cured the issue. It was much better, but I still got a damp headlining in the rear corners but only after really heavy rain... took a lot if investigating with hosepipe and phone camera to record the leak and I found it was coming from the same place yours appears to be; the top corner seals of the rear windscreen. I did this;

WilmslowSi · 8 Apr 2025

dammit pressed enter!

I unclipped the roof runner plastic trims gently as they approach the rear of the car and cleaned underneath them and also around the inside edge of the rear window seals, sort of lifting the seal flap up and getting a cloth with ISO alcohol on it between the body and the seal to get all the gunk out, I did this around each top corner and about 8" either side of it. I then got some 4mm and 9mm butyl rubber tape, heated up a chunk of 9mm and pushed the blob firmly into the corner, using the space created by the lifted roof channel trim... sort of pushing it into all the nooks and crannies of the corner but all underneath the rubber seal.. I then ran an 18" length of 3mm butyl underneath the rubber seal around each corner in the areas I'd cleaned.... gently heated the area and pressed down on top of the top rubber seal till everything was tight and flush again - could not see any of the butyl at all. I then reclipped in the roof runners but slid them back a little bit to make sure the very end slipped just under the rear windscreen seal by about 2mm (previously I had a small gap). It has not got a drop inside since and I know that the butyl strip comes out easy if needed and is not messy or bonded like silicone sealer.

t911r · 8 Apr 2025

WilmslowSi said:
dammit pressed enter!

I unclipped the roof runner plastic trims gently as they approach the rear of the car and cleaned underneath them and also around the inside edge of the rear window seals, sort of lifting the seal flap up and getting a cloth with ISO alcohol on it between the body and the seal to get all the gunk out, I did this around each top corner and about 8" either side of it. I then got some 4mm and 9mm butyl rubber tape, heated up a chunk of 9mm and pushed the blob firmly into the corner, using the space created by the lifted roof channel trim... sort of pushing it into all the nooks and crannies of the corner but all underneath the rubber seal.. I then ran an 18" length of 3mm butyl underneath the rubber seal around each corner in the areas I'd cleaned.... gently heated the area and pressed down on top of the top rubber seal till everything was tight and flush again - could not see any of the butyl at all. I then reclipped in the roof runners but slid them back a little bit to make sure the very end slipped just under the rear windscreen seal by about 2mm (previously I had a small gap). It has not got a drop inside since and I know that the butyl strip comes out easy if needed and is not messy or bonded like silicone sealer.

Ohhhhh I'll try this, so do you mean here:

WilmslowSi · 8 Apr 2025

WilmslowSi said:
dammit pressed enter!

I unclipped the roof runner plastic trims gently as they approach the rear of the car and cleaned underneath them and also around the inside edge of the rear window seals, sort of lifting the seal flap up and getting a cloth with ISO alcohol on it between the body and the seal to get all the gunk out, I did this around each top corner and about 8" either side of it. I then got some 4mm and 9mm butyl rubber tape, heated up a chunk of 9mm and pushed the blob firmly into the corner, using the space created by the lifted roof channel trim... sort of pushing it into all the nooks and crannies of the corner but all underneath the rubber seal.. I then ran an 18" length of 3mm butyl underneath the rubber seal around each corner in the areas I'd cleaned.... gently heated the area and pressed down on top of the top rubber seal till everything was tight and flush again - could not see any of the butyl at all. I then reclipped in the roof runners but slid them back a little bit to make sure the very end slipped just under the rear windscreen seal by about 2mm (previously I had a small gap). It has not got a drop inside since and I know that the butyl strip comes out easy if needed and is not messy or bonded like silicone sealer.

WilmslowSi · 8 Apr 2025

tr87 said:
Ohhhhh I'll try this, so do you mean here:

Yeah I've just nipped out to take a couple of pics of mine to show you what I mean. I think part of the inner rear window seal is perished so when water builds up it just finds its way through. The proper fix would be of course to replace the seal but this butyl stuff is cheap and easy to work and appears to just 'help' the seal a bit without all the bodgery and mess of silicon... if you heat it it goes tacky and takes the shape/fills gaps, but once cooled you can just pull it out easily and try again.

t911r · 8 Apr 2025

WilmslowSi said:
Yeah I've just nipped out to take a couple of pics of mine to show you what I mean. I think part of the inner rear window seal is perished so when water builds up it just finds its way through. The proper fix would be of course to replace the seal but this butyl stuff is cheap and easy to work and appears to just 'help' the seal a bit without all the bodgery and mess of silicon... if you heat it it goes tacky and takes the shape/fills gaps, but once cooled you can just pull it out easily and try again.

Ah thanks, I'll give it a go, what I can't believe is that I have had the rear screen out and rebonded in professionally and new Porsche rear seal and trim and it's still leaking like before!! I'll have to trust in Butyl then!

WilmslowSi · 8 Apr 2025

tr87 said:
Ah thanks, I'll give it a go, what I can't believe is that I have had the rear screen out and rebonded in professionally and new Porsche rear seal and trim and it's still leaking like before!! I'll have to trust in Butyl then!

It's a bit of a bodge of course, but I was losing patience with the musty smell so thought I'd give it a go and so far it has worked for me so hope it does for you too!