The new ring and pinion I installed is calling for 75-140 synthetic gl-6 or higher rated , instead the 85-90 regular gear oil for the rear end.The manual trans uses the same fluid as the rear ....would it be ok to switch the manual trans to the synthetic 75-140 also?
or maybe use a lighter synthetic closer to the original weight for trans ,if the weights even cross over between synth and regular oil?