Hermes hit the nail on the head when he decreed oil choice to be a popcorn question...Well.... get it out then.. (-:
When I did a bit of spanering for a m/cycle racing pal way back when, I ever remember the smell of Castrol R that hung around the race tracks of the time, mostly used in old Manx Nortons Velocette Thruxtons and other older bikes which by the day were becoming outnumbered and outperformed by ever more Jap machinery turning up at events... "R" was a vegetable based oil and stuck to everything leaving the usual incontinent old Brit engines looking a tad messy at times. Often folk would put a drop of "R" in the petrol tank of their street m/cyles to give of that very definite aroma of running on "R"... (-:
I can remember well when Duckhams Q guys turned up at the tracks telling us this wonderful new thick and green looking oil was quite the best thing for ALL machinery, even the old "R" addicts gave it a go.. From a dull memory Castrol not long after came on scene with GTX... though a friend used it and ended up with a degree of emulsification visible on the underside of the filler cap, and changing to "Q" that quickly cleared up so we stuck with Duckhams Q for as long as it was available.
By the time I was into Porsche by way of a 69 912, the recommended oil was Castrol CRI 30 according to my Haynes manual ... But then I suspect Haynes may have had an arrangement with Castrol at the time... dunno for sure. CRI 30 was not readily available and at the time folk were FAR less fussy about oil, me included, it was an air cooled engine and my bikes did well enough on Duckhams so that would do.... and it did.
Moving on a few years till I bought my first 911 an SC and I was a tad more fussy about using Porsche approved lubricants, which I did, sorry can`t remember what it was... Duh! though anybody with a 77 SC could find it in their handbook... Then Porsche decided that Mobil 1 was the oil of choice for all 911`s... I was concerned enough to write to Porsche being uncomfortable with what seemed like a sudden change in brand and type of oil , they did reply with more than enough information to confuse me into submission...
By the time I gave up on Porsche for fun mileage and became a born again biker circa the late 90`s such was the changes in engine design and materials used, that choosing the correct oil seemed to have become a bit of a minefield... Much as it still seems to be today...?
You can still buy Castrol R and other "Classic" oil in classic cans, and no doubt at Classic prices, however I do remember buying a Ford with no gearbox drain plug... My first education relative to filled for life design, which it seems has moved on to a stage where it seems it is possible to re-use some synthetic oils time and again if you send it off for cleaning in order to re use it...!!!!
All of which causes me to wonder exactly where we might be in terms of best protection in terms of lubricant choices.... It seems Porsche were pushing Mobil 1 in the 90`s for everything air cooled up to then, so I guess the 3.2 Carrera and Turbo fell into that grouping too..?
Ok so I`m now into unknown territory, I`m guessing that the 964 although air cooled is hotter running engine than those that came before though obviously still air cooled but with cats (?) which may have added to the possible rise in temperature related to trying to create a more lean burn situation to improve upon emissions, and thus it also seems logical(?) that an engine running significantly hotter might benefit from an oil more suited to running in a different environment from all it`s previous air cooled brethren...? If any of that adds up, then it would seem the 993 would perhaps have the same grade of oil recommended...? I guess the answer is to be found in your Porsche handbooks supplied with your cars...?
As for those who wish to recommend other oils.... Hmm, do they have a deal with a supplier or are they really experienced in rebuilding Porsche engines and seen and monitored the effects of different oil use within engines they have a good idea of the way they have been run before being stripped....Hmm..?
As for Porsche dealership recommendations ??? I suspect they are up to their ears in watercooled maintenance and have been for many a year now, so who knows what they might suggest is THE oil to use in any air cooled Porsche...? Thinking back to the days of Mobil 1 for everything..? What about indy`s do they carry different oil brands for different cars or is it possible they may have a supply arrangement.... after all business is business..and it can be a serious business...?
Were I running an air cooled Porsche up to the 3.2 generation, I guess I would be using Mobil 1 if still available or whatever modern equivalent thereof....I am old school thus would be changing my oil annually regardless, of much else......Though admitting that Chief is probably correct that doing so may not be necessary, but a bit of overkill could be considered as a reasonable
Insurance given the cost of even a partial rebuild..... But I am keen to learn from anyone who thinks differently and why they do so....(-:
If you are going to nail your colours to the mast on an oil type/brand then I suspect you may be best to be sure you identify your engine type...?
As ever, just thinking in type..