you know who you are... the hard ridin' , and many years old  atv owner that probably has a cracked tank fuel gauge... That  never sits in a shed?

Guess where all the rain water goes?  Yep... to the lowest part in the tank.. and next time you need to use 'reserve'.. it'll be a long walk home.   
as long as you never  switch the valve to reserve,  it's hardly a problem!    
So either replace it, or  I just  smeared some spare  polyurethane (windshield glue) over the top.   RTV isn't going to last very long.