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As stated in the question, I would guess the valve is about 17 years old.
No worries! :-)
I was thinking along the same lines. I just wanted to make sure it wasn't something easy to work on myself. Replacing the valves sounds like something I should leave to the professionals.
Fortunately, I can survive with washing laundry in cold water for a while (well, really tepid here in Phoenix). Thanks for the advice.