Right, "regular" 75w90 GL4 gear oil, not redline synthetic. Isn't Mt-90 a full synthetic ?

Anyways haven't tried the heavy duty Redline products, though I would try them before going to MTL or MT-90. Over the 10 years of driving DSM's I found MTL/MT-90 to be crap. They work fine for small horsepower applications. JMHO and personal experience.

There's castrol synthetic 75w90, MT-90, Amsoil, and other 75w90 GL4 gear oils too.

I've tried everything, I'll stick with my motormaster blue bottle , and special blend now.

Don't want to go into too much details, but just stating what works fine for me with the power I make, and no broken internals yet on a stock trans.

Feel free to use all the MT-90 you wish , everyone has a different opinion. I know it sounds weird, but anytime I used a straight synthetic, it just never shifted the best.