Leaky fuel tank at sender..

I am ready to start banging my head against the wall.

Last year, when I re installed our gas tank, I bought a new seal, cleaned up that section of the tank and re installed a new sender. It leaked when the tank was filled past the sender.

So I decided to replace the sender since we were going to pull the tank anyway.

Pulled/drained the tank. Took it off. removed the old sender. Cleaned around the sender even though it was quite clean. Installed new sender and another new gasket. Did a quick test. No leaks.

Filled up tank. All was ok. Went out this am..lost 1/4 tank of gas and you can smell it gas quite easily..

Re doing the steps above again would be an excessive in futility...

Any suggestions ?

Thanks
Ian.