Yours owners manual contains operational information.

The CD-Rom's are digitized versions of paperback repair manuals. Mercedes produced a "Maintenance Manual" for cars from 1981-1993. It contains instructions for tasks such as fluid/filter replacement, etc. This manual is included within the CD-Rom for 126 cars. Don't know about 124s.

If you plan on doing repairs/maintenance, you're going to need documentation. The CD-Rom is loaded with information.
Some complain about ease-of-use, or the lack of it. It takes awhile to get used to, but it's all there with the exception of transmission repair.

I believe this site sells the MB CD-Rom's.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"