What grade of oil would one use in a 1989 Porsche 928 S4, automatic transmission, 100K? I say Mobil-1 "extended performance" synthetic
15W-50 is the best bet, though the opinions vary on this widely. The "extended performance" synthetic that Mobil-1 has is (at the moment) hard to find; does anyone know where it can be found online?Is 10W-40 too thin for the 928? Reading misc websites I've seen people recommend from 5W-30 to 20W-50, so I'm understandably a bit lost on the issue of grade. But at 100K, I personally lean towards the thicker oils.
I will be (likely) purchasing this exact car shortly. Is the Fram (PH6583) oil filter acceptable for use in this car? It supposedly is, though the other (foreign-manufactured) OFs seem to be much larger. This car requires 9 quarts of motor oil, am I right? The Fram PH6583 seems too small. K&N doesn't make an oil filter (that I'm aware of) that fits this car; what manufacturer/model would be best so far as oil filters are concerned?
Also: Is synthetic ATF a good option for use in a car of this age/miles? Mobil-1 sells one, though I don't hear nearly as much talk about synthetic ATF as synthetic motor oils. Are they of any conceivable advantage?