heater fan problem solved!
Thanks for the suggestions, guys. After doing a search on similar problems on this site, previous posters suggested checking the SEPARATE fuse outside the main fuse box and on top of the shock tower.
SURE ENOUGH, the 30 amp strip-fuse located just in front of the main box was cracked in half. Replacing it resulted in an immediate resumption of fan motor!
Anyone having a similar problem needs to be aware that the fan motor fuse for the heater is not included in the climate control fuses in the main box but is separate and by itself. (Now why would Mercedes DO that?)
Any other hidden fuse locations I should be aware of? Thanks for your help.