Thanks for the link Bob... I remember that thread and was going to look it up if the shutter was beyond my abilities to repair. I overhauled it myself about a year ago. I have experience with clock and watch repair, but this was my first sincere attempt at shutter overhaul.
I just had a chance to open it up and give it a look over. The mainspring is intact, but somehow "jumped out" of it's anchor hole. Very odd. There doesn't look like enough space for that to happen. But, whatever... Thank goodnes I have the Compur repair manual -- it makes it much easier to figure out what's going on!
It's now working again, and I'm happy. (But I'll certainly be a bit leery as I run the next roll of film through the camera!) Maybe I should consider sending it out for a professional overhaul, eh?