I suspect that the answer to this one is to buy a new one, but I thought I'd
try.

It has periodically slowed down to a crawl when refilling the tank, and at
best, by turning the feed valve on and off, I have gotten whatever seems
to be plugging it up to clear. That's happened a couple of times, but now I
can't get it unplugged.

I can't find any specifics on the mechanism, just installation
instructions. Is there a way to disassemble the valve and fix the problem,
or isn't it worthwhile?