When I had my tanks out in 1999 for the paint job and hose replacement,
I also noticed stains from the sending units downward. I decided to
replace the gaskets and reseal the things "while I was at it". The local
wrenches said that getting the screws around the sending unit to seal
completely was a crap shoot and the recommended method was to coat them
with fuelube. They also said they were trying out using statoseal
washers on the screws in an attempt to keep the screws from leaking.

When I had the sending units out, I noticed that the resistive element
had holes for rivets at both ends, however, only one end was riveted on
both sending units. I thought it was odd but was not about to
"experiment" by replacing the other rivet. My mechanic agreed. What was
also odd was that the resistive element could wiggle back and forth
pivoting on the single rivet. It struck me that eventually that would
break from fatigue. But, I found no remnants of rivets in either tank
and was hesitant to do any modification to this important system.

Put everything back together and all worked fine for about 3 years or
so. Then, the right gauge began reading about 2-3 gallons lower than the
left gauge with a level plane and the same amount of fuel. It continued
to read low by anywhere from 2-5 gallons low for about the next 2 years.
Then, one day, the right gauge read 0. Really less than zero and on the
peg. Getting out the repair manual, I saw that zero resistance should
send the gauge to the "full" peg. I briefly grounded it and it did jump
to "Full". For the next year, it worked as it had (around 4 gallons
low). LAst couple of flights, it began reading all over the place, from
less than zero to a few gallons low. Again, I briefly grounded the gauge
and it flew up to zero. But this time, if remained flaky and is reading
all over the place.

By switching the sending units to the opposite gauges, the problem
appears to indeed be with the right sending unit (or the wire from the
terminal block to the sending unit). Checking the blade connector at the
wing did not have any effect.

I cannot remember if there was enough of a hole to get at the wire on
the sending unit when you removed the inspection panel at the right
landing gear. My hope is that the wire has worked loose at the sending
unit terminal. I seem to recall JUST being able to touch the terminal if
I put my arm in it up to the elbow (and it was NOT easy).

Anyone else have any experience with these critters? Are they supposed
to have 2 rivets holding the resistive element(one at either end)? Can
you get at the terminal without pulling the tank? Are new sending units
available for a reasonable price (maybe $200 or so)?

Thanks for any suggestions. Please restrict any feedback to actual
experience.

Mike