My ventilation fan quit on our '91 300E about six months ago. I did the same checked fuses etc. I was dreading the fan motor replacement.
It turned out to be the fuse link. Its holder is about an inch long, about a 1/2 inch wide. It is an odd black plastic part near (in front of) the fuse box. It has two fairly heavy-duty wires going into it, one on each end.
Pry open the cover and inside you will see what looks like a flat piece of metal. These fail and will even look to be OK.
I might have a picture of its location if you can't find it.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)