What are the tips made of? Chrome plated/polished stainless/anodised etc. I have standard 993 S tips which seem to be anodised ith a matt finish and get decent results from autosol type paste.
working for a household goods manufaturer as i do i finally feel qualified to help on this thread
OK, oven cleaner can be used depending on the type. Acidic cleaner (such as cillit bang) will clean nicely but be careful not to leave it on there for any length of time as it will tarnish (as our cleaner has done to our bathroom taps... harumph). I'd leave agressive alkali based ones alone for stainless steel (mr muscle etc) as they can be very aggressive on metal surfaces (shiny ones anyway)
Personally i'd recommend Silvo (liquid or the wadding) or brasso (you can laugh) as a first pass and then maybe cillit for any more diificult stains but like i say, rinse thoroughly and don;t leave it stewing on there. Oh and don;t do it on hot exhausts either...
I do have knowledge after all... sadly in cleaners rather than porsches...
Like others here I use Autosol and a bit of elbow grease (initially). Brings em up like glass. If you give them a quick buffing every so often with your Autosol rag after that, should keep them looking good.