Fuel gauge check

A little dab of lubricant (Vaseline, ATF, KY, grease), just enough to coat the O ring, will let the sender slide instead of grab the O ring when it tightens down and prevent a leak. If the sender grabs the O ring it will bunch up and you will have a gas leak at the lock ring. The sender will twist a bit when you tighten the lock ring no matter what you do.