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.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician