CASTROL oil for tranny/diff

Originally Posted by ZoomZ

Also, Not sure how Motul gets an oil to perform GL4/GL5 work, but nottheless, our MT transmissions require GL4.

GL5 contains Limited slip Friction additives that eat "Yellow" metals like Brass, Bronze etc. I believe the Synchros in our MT have yellow metal.

For that reason, I'd also steer away from the GL5 ratings.

Regular Gear oil will be either 80W90 but if you go with a Synthetic, it will become USUALLY 75W90. Same would apply to other weights. So you are ok with those grades.

Originally Posted by 40 to 332

This piqued my interest. So I checked the technical specs for Motul Gear 300 and, according to Motul, it is suitable for all types of seals and yellow materials used in gearboxes. Presumably, the sulphur additive they use is buffered to prevent/reduce any brass/copper components in the tranny from sloughing off.