Best manual for W126?
 

I did a search and found out that you can get service CD's for these cars. They are expensive so before I buy them what do they cover? Just the engine, or do the cover the whole car. I need a good manual with diagrams so I can figure out this car. The diesels the simple part!
PS. The cars a 1987 300SDL with the OM603 not the OM617.