i recently had a no crank issue with my benz, which is a 93 m104 2.8.

The problem turned out to be the #5 fuse. Although the fuse was not burnt out, there was some oxidation on the fuse tips ,which caused an open circuit, and prevented the engine from cranking.

Make sure that both the #5fuse and contact points in the fuse box are oxidation free.

good luck