dumb question: sender gasket

RedFish said

Yep, gasket goes between the tank and the sender. If you have a OEM lock ring, use it.
Many of the aftermarket lock rings are made of thinner material and will cause a leak.
When done right it wont need any sealant and it wont leak.

Click to expand...

The lock riing I got with the Canadian "good" tank was also slightly too small, and slipped through the tangs, also causing a leak.

Use the one from your old tank. It's a MUCH better fit.

...and think about it, tank/gasket/sender, or else...