In 1992 Porsche factory fill on all models was 5w40 (Shell)
In 1996 Porsche aligned with Mobil 1 and revised oil viscosity chart recommendations to include using synthetic oils.... Dino 15w40 or synthetic 5w40.
In 2001 Porsche approved using 0w40 or 5w40 synthetic engine oil for
all Porsche models 1973 to 1998.
Rotella T6 5w40 has a good dose of ZDDP: see the virgin oil analysis Rotella T6 5W-40 manufactured 01/27/12
