I have a 300D 2.5, 124 chassis - anyway, had the same sort of issues and it turned out to be a overvoltage protection fuse. This fuse, and a few others like it, are not in the fuse box. Look behind and around the battery (front passenger side on a 124). Also, get behind the battery, between the battery and the firewall (at least on a 124) - there are some fuses there.

Might help. Might not.

Also, using mobil1 synthetic fixed the cam follower issues on this car. Try that first before replacing, you might be surprised. Takes a few hundred/thousand miles though. I am totally sold - I only use Mobil1 from now on.