An easier way to tell if the aux fan fuse is blown is to see if the rear window washer (not wiper, washer) is inop. They are on the same fuse. Of course, it could be the rear washer pump is blown or you are out of washer solvent (what, another leaky tank!?), but the same can be said for the aux fan of course. Just because the fuse is NOT blown doesn't neccesarily mean the fan motor works.
Incidentally, speaking of washer tanks, the original 5 liter washer solvent tanks are now unavailable from Mercedes, you have to install the newer style 7.7 liter tanks. Which aren't a whole lot better, just larger.
Gilly