An update:

I got a junkyard fan. Although it looks like an earlier version, it came out of a 123. It spun easily, but caused the fuse to get hot anyway. So I pulled my original fan apart and replaced the brushes and oiled the bearing, put it back in the car. The fuse still gets hot to the touch on the high fan setting only. The air flow thru the vents is considerably weaker than it was pre-fan-rebuild.

I put a one amp fuse in the black wire leading to the aux water pump to protect the new CCU.

I've read elsewhere on the forum that the MB blower fuse shunt kit is meant for w124's, and that it should not be used on 123's. Does anyone have experience with this on a 123? And would it be a good idea to put one in, or just spring ofr a brand new fan?