Yep, one final search for a decent transmission oil before I have to go to the Porsche dealership.
The MAIN reason that I believe there is a suitable substitute for the (GL4) Porsche gear oil, is that I am pretty well-versed in Audi manual gear boxes, and IMHO, there is probably almost no difference between the 6 speed transaxle (Audi 01E) in my project car, and the 6 speed in my Boxster S. Both manufactured around 2002.
I currently have the Redline MT90 in my (Audi) gearbox, which seems to work fine, but one thing that has always bugged me is that while Redline recommends it, they also say that is is NOT for use in boxes with hypoid gears. The ring gears in both my Audi box, and the Boxster box are both hypoid gears.
Here is the Redline oil info...look closely, and you will see the disclaimer about hypoid gears...
Red Line Synthetic Oil - Gear Oil for Manual Transmissions - MT-90 75W90 GL-4 Gear Oil
Anyway, here is the info on Ravenol. Let me know what you think!
RAVENOL Motogear SAE 75W-90 GL-4 - Ravenol
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