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1990 964 Gear Lube Recommendations

Transmission and Clutch

Vehicle Information: Year: 1990; Body Type: Convertible; Total Mileage: 80000;

Looking for some advice on proper gear oil for a 1990 C4. The owners manual specs out 75W90 GL5 and I have read in various articles and on web sites that use of synthetics are too slippery for the synchros, other have said synthetics work just fine. Some say Swepco 201 is ok, others recommend it for just 915 transmissions. Redline 75W90 synthetic states "not recommended for use in synchro transmissions due to extra slipperiness" and it has the GL5 rating. It is getting very confusing with all the products on the market. With the G64 transmission with the limited slip and front differential I want to do it right the first time when I change the gear lube.

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