Make sure you do not use a gear oil that is multi functional rated as in GL4 and GL5 combined. It must be straight GL4. I recommend a product from NAPA called STA LUBE. Item number SL 24239 SAE 85W90 Hypoid API/GL$ (Distributed by CRC) Robert L. Gannon http://home.comcast.net/~trsix74/wsb/index.html