87 bayliner capri cuddy - replcae gas tank55 gal 1986?
 

I was removing my plywood floor for rot inspection and found the gas tank is
the original. It
is full, so if I need to inspect underside, I would have to drain 55 gallons
and remove the under seat framework assemblies.

How else can I tell if I need to replace/repair the tank without removing
it?