I've had good luck with the fuses in my Volvos (the same fuses as in the MBZ) as follows:

1. Disconnect battery
2. Remove fuses and clean the fuse clips with a fine emery cloth.
3. Lightly coat the fuse clips with a silicone grease such as Syl-Glide
4. Clean the fuse tips, replace any with broken tips, and coat with the silicone grease.
5. Reinstall the fuses and connect the battery.

Since I started doing this several years ago, I've never had a fuse problem. I used to have them often.