...the OEM grease for a 1991 BMW 535i ? It is important not to mix grease of different bases. I dont want to remove all of the existing grease because i dont have repacking tools. What type of grease is existing in the bearings (front wheels)?

ummm dude seriousy yer thinking wayyy to hard...get hi temp wheel bearing grease and slather it on and its all good...even a yugo can run on beamer grease ;)

Only two types of grease in automotive bearings High and Low temperature the other person is right just put high temperature and you can't go wrong. What they mean by not mixing is that if you application requires low temperature as a minimum putting high wont hurt it, but if your application requires high and you put low than you are for premature damage. Thats all is meant by not mixing, there are other types of grease but for different applications and won't be sold just over the counter either. The reason they sell High and low and not just HIgh is savings High temperature should cost 25% more at least because is at least 25% effective at the same temperature.