High quality with the correct viscosity - anything else is personal preference. RedLine MTL or even a mix of RedLine MTL and ATF.

 

What is the correct viscosity?

 

I guess the transmission is ZF 320Z that normally comes with 5-speed E46 330i.
BMW oil for this transmission is Castrol Syntrans B75W GL4. It's normally available here in Europe.
Don't use GL5, some metals in this gearbox don't like GL5.

RedLine is an American thing.

 

look it up on the website of Kroon, Champion, Mobil, Castrol, or even realoem.com might have the correct viscosity (not 100% sure on the latter)

 

I have a ZHP wit the manual 6-speed. I went with the Redline MTL as recommended and it became more difficult to get into 1st. I quickly switched to Royal Purple Synchromax and am VERY happy with it. I believe that there is only 1 viscosity

 

Thanks very much guys 😊

 

The viscosity is 75w/80. I use BMW's MTF-LT-2. IIRC Pentosin also has MTF2 which is OE.