It appears I have a dead spot at about 1/8 full. When it gets to
that level, the gauge suddenly goes to well below empty. But a
while later it comes back up to the right reading. Always happens
at the same spot, so I would assume there's a bad spot in the
sending unit. By the way, when the gauge goes to zero, the fuel
warning light does not come on, so it appears that's a separate
sending unit and circuit, which is a bit surprising.

Anyway, I wonder if I can remove the sending unit from the tank,
inspect it, and possibly scrape the crud off and fix it. That would
require being able to re-use whatever gaskets or seals are involved.
Can anyone with experience in this area tell me if I can do this
without having to use a new gasket?