Creeping green fur.... My ribs are still killing me from laughing so hard....
Well guys, here in New York,we call it the copper crotch rot....
Lets see.... Older car, euro fuses, lots and lots of rain, and creeping green fur.... Sounds like your main fuse holder assembly is going green furry.....
Get a dremel moto tool and some heavy wooded stick Q-Tips. The dremel must be a variable speed model. Get some medium grit valve lapping compound from a good auto parts or tool place, NOT STRAUSS OR PEP BOYS...lol Chuck the Q-Tip in the dremel, put a tiny dab of lapping paste on the cotton, and go to town. After both ends are burnished and shinny, spray the ends with contact cleaner to remove grinding compound debris. Also, very Gently bend the fuse holder contacts inwards to re-torque their tension. Cut the Q-Tip very short, about 3/8" and it should tighten enough with the std.1/8" collet installed. Use very little compound, its very powerful. Just a wetting is enough. Remove one fuse at a time from the fuse box, and lap the socket end of all your fuse holder clips. Take "CROCUS" cloth, and polish each end of everyfuse, or better just install brand new ones. If the Q-Tip trick seems too much for you, just wrap a pencil eraser with some small strips of 320 wet-dry sand paper, and start scrubbing. Use contact cleaner as a lube to do this. After you do all the fuses, you can then start on all your plug in relays and modules, behind the fuse holder assembly. A card-board nail file using only the fine side is good for cleaning all those connector tabs on the relays. (Finish with contact cleaner sprayed liberally on the tabs, holding the relay downwards.) Finally, take off both battery terminals, and with a battery terminal cleaning tool, polish up the battery posts and clamps. let us know how ya make out.....
dave....
PS: Do a very careful ground strap inspection, especially at the eyelet connector ends. Check all around. If any at all seem greenish looking, replace them.

1993 300TE 4Matic 186,000 miles