Have you checked all the fuses? Not just the ones in the fuse block, but the others in the separate boxes on the firewall. Not exactly certain on the 123, but look on the firewall, right side and see if you have several black boxes. In these boxes are more fuses, just left the top of the box off (one has a screw holding it shut) they each hold two fuses. Two boxes are for the windows, one may be for the radio, and the last could be for the blower (it is for the A/C blower on the 280 [separate blowers A/C and heat for me]).
Could be the brushes are bad, have read about folks simply replacing them. Could be the blower just needs a little push to get started again. Lots of free or almost free things to try first.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.