If your mechanic is a real MB tech he will want to purchase MB WIS (workshop information system). It is about $2800 and is a years subscription with 12 updates. It doesn't time out though so it covers a moment in time.
For your own purposes the "Introduction to Service" manual for chassis 129 would be the tool. Buying each model year between 1990 and your year will give a few extra bits and pieces. There are training CDs that appear regularly on ebay called "info access". There is one on the 129 chassis.
Bosch Master, ASE Master, L1
33 years MB technician