Al - I don't think it was a handle / diverter seating issue. That all seemed fine - except if the pressrue was allowing it to rise up & unseat *just enough*. It's the only thing I can think of that makes any sense. If this doesn't do it, I'll have to replace the whole stinkin' valve. That's an end of season / shutdown for winter plumbing job.
Gotta laugh... if I don't I'll post a "For Sale" sign in the front yard...