I used Royal Purple Synchromax in my E39 540-6 & was happy with it.
I get conflicting input on their transmission oils for my E34///M5.
One rep states to use Synchromax for transmission & Gearmax 75w90 for differential.Another states Gearmax 75w90 for both.

In Roundel Mike Miller dismisses the product,because the name reminds him of a candy or drink from the old fasioned soda fountain shop.

What is the right RP product for this application.

'91///M5 Blk/Blk Coming out of winter storage.