
Well, it had to come from somewhere, and a little examination showed that the problem was that the v belt has been rubbing on the molded hose that connects the expansion tank to the water pump.

I'm sure it didn't always rub together like that, so I'm going to have to find out why it started doing it. You can't see in the picture, but there is a pretty deep gouge cut into that hose, and it probably should be replaced. Does anyone here know a source for a replacement? If not, I'll have to make one up from standard bends and connector tubes, but I'd rather not if I don't have to. The original is a complicated molded part, and I'm sure it won't be easy to find.
Tom