i have always liked Mercedes and i finally got one i got a 1991 300SEL with 3.0L gas engine.

it has 175k miles all stock. i am curious how long before i will have to do any major work like replace motor or transmission or anything?

and also i can not figure out how to turn the a/c to vents i have already done a R-134a conversion and it blows ICE COLD but only on the top of the dash defrost vents, i cant seem to turn on the normal passenger vents... i just dont know all thes buttons? anyone able to help me?
below is a picture of my dash setup not MINE was an online picture but it is the SAME setup

http://img296.imageshack.us/img296/2029/console3on.jpg