I just went through this on my 124 last weekend. Fan was working fine, stopped for dinner, no fan. I've got it working again, but haven't really identified a cause. It was one of those take out, test it, it works, reassemble it, it works kind of scenarios.
The most likely problem is worn comutator brushes on the motor. You can probably extract some more life from the fan by taking it out and cleaning up the brushes. Quite likely one of them cocked at an angle and lost contact. Alternatively, the brushes can be replaced for a modest sum - plenty of threads on that topic here.
Pulling the fan motor isn't too bad a job. Perhaps 2 hours the first time, much, much less once you've done it.
Best of luck,