We just got our first Bombi, been going through it mechanically. I'm asking the same question because I see a hypoid ring and pinion in there with the wet brake bands. The hypoid gears call for 90W EP, GL-5 oil, the brake bands call for TDTO. I'm guessing it might be better to go with 30W or even 50W TDTO oil. But then will it flow thru the filter/cooler?
All the other diffs I've worked on have spiral bevel ring and pinion, much less sliding action.
-Pat