I'm installing really soon Helix SMF kit and need to solve chattering problem with SMF kits. So I was told that 75w140 oil for gearbox solves the problem completely, so can I put that in my S3, engine code is BHZ ?

My friend has Castrol TAF-X 75w90 in his S3 (and he has also Helix SMF set) and chattering is pressent only on idle, not while driving. Other friend has GTI ED30 with same kit and on his car there is too much chatter even while driving. But he has stock oil in gearbox ! And no rear wheel drive, so maybe that is also reason for much more chatter because there is less tension on gearbox.

So which oil can I put in this gearbox, which are standards ?

Tnx for help !