>I must have completely missed earlier discussion on this problem.
Yep. After a couple of years of autogas in my tanks I had an interesting problem that led to the same discovery -
During pre-flight I noted that the right tank fuel level was 3/4 full when I checked the sight gauge. I always remove the fuel caps and look in the tank. When I looked in the right tank I couldn't see any gas. Using a flashlight I saw that there was about an inch of fuel in the tank - but the sight gauge was still 3/4 full of fuel - and they say you can trust a sight gauge because you're actually looking at the fuel! Don't believe it.

The bottom hole in the white plastic had swollen and become blocked, so the fuel couldn't exit the gauge. When I removed the gauge I found that the white backing was very soft, but in my case the clear plastic part of the gauge was unaffected. I replaced both gauges with new ones from Vance, and added his new metal inserts to stop the holes getting blocked. That was last year. I regularly tap the plastic to be sure its still hard. No repeat problems yet.

If someone comes up with a totally fuel resistant replacement I'd love to have a pair, but in the meantime these seem to be holding up, and it only took a couple of hours to change each one. Those yet to install gauges you've had on the shelf for a while - I suggest that you order the little metal inserts from Vance - they could save you making decisions based on an incorrect fuel reading. Those flying without the inserts - adding a visual fuel level check with the cap off to your preflight wouldn't hurt.

My 2c
John Slade
Turbo Rotary, N96PM
96hrs.