hello vaclay,

I recently had to deal with the same exact problem, however my car is a 300E.
In my case, the #5 fuse in the fuse box had corrosion on it, and it caused the no crank problem. NOTE: the fuse was not burned out, but rather the corrosion on the fuse caused an open circuit situation which resulted in no crank, so check your fuses closely. Some forum members even suggest replacing all the fuses with new ones.

While researching the problem, i came across the following link, which may be of some use to you: http://www.aa1car.com/library/voltage_drop_testing.htm

here's a good video on voltage drop testing as well : http://www.youtube.com/watch?v=v0THDAS1nws

If I remember correctly there's a thicker wire which runs from the battery + terminal all the way to the starter, and the starter ground is achieved by a ground strap/cable which connects the frame to the engine/bellhousing. Make sure that both of these cables are corrosion free aswell.

good luck