Thanks Bob. Giant RV in Murietta, CA (about 25 miles from us - we're at Jojoba Hills SKP) found the part and will have it by late this afternoon. The motor - part number RAP 90311 - costs $276 (plus $22 tax). HWH wanted $284 plus the cost of overnight shipping.
I made one final test. I had my DW hold the generator slide switch in the retract position with the HWH system energized. I rapped on the starter housing with a hammer. Every time I whacked it, it ran for a few seconds. I was able to retract the generator slide after several whacks.
Now, I'm totally confident that when the new motor is installed tomorrow, I'll be able to retract the slides and hit the road.