Motul 4100 15/50 or castrol 20/50 should do the job.since the B8 is quite old and
quite tired from hard accelerating through the years. Gearbox- any normal mineral
oil but change every 20,000.00 and the car will be fine. Make sure the alternator
is working well for the rev range and power supply, try the Pivot voltage
stabilizer (make sure original unit) ,this little blue box of magic has really been
outstanding and helped a lot of engines from brand new to old. And always
keep ur engine clean ,dirty engines can overcome a lot of heat. And never
use an additive in ur engine oil,just change the oil regularly and use the
same brand always. maybe for the gearbox u can try an additive of some good
reputed brand.....Good Luck