Fuel leak could be relatively simple.  Once you find the source of the leak, use a venturi vacuum device attached to the fuel tank filler cap, make sure the vent is blocked and the fuel line is turned off at the valve, (DO NOT USA A VACUUM CLEANER as there will be too much suction AND the danger of exploding fuel vapors as thy are drawn into the vacuum cleaner motor).  With the vacuum applied to the tank, apply some epoxy with a bit of flox mixed in and allow it to be drawn up into the leaking area of the tank.  As soon as you're convinced there is sufficient material drawn into the leak, remove the vacuum pressure and allow to cure.  I've heard this works.

 

An alternative to the above procedure would be to remove the wing and use sloshing compound internally with a slight pressure applied momentarily to the tank to force the stuff through the leak.  Pour out the excess compound and allow to dry (cure).  Be careful to not get this compound into the fuel pick up point where the fuel leaves the tank for the fuel valve.  Usually there is a finger screen in that area and if the screen becomes blocked then no fuel gets out of the tank...