Yes I think my issue and what was confusing me, I confused two different red line oils. I thought that they were recommending the same for both. But redline actually recommended their gl-4 75w90 "mt-90" for the manual. And their 75w90 gl-5 or redline 75w90 gear oil. Two very different red line oils... Which I had confused as the same.

So I am considering using the Pennzoil synthetic 75w90 gl-5 full synthetic in the diff. And Mannol 75w80 mtf-4 in the trans as it meets MB 235.10 specs. Both which are quite inexpensive yet the quality is very high.