The tank on my Tomos TX-50 was rusted out. It eventually devleoped pinholes. I patched over them with fiberglass which held for awhile. Then it started leaking again. I eventually found a good one off Ebay and replaced it.
Fill it with Evapo Rust, flush it out with water then something like kerosene, mineral spirits, acetone, laquer thinner. Whatever kind of solvent you have laying around. Sand off the paint then patch over the holes with fiberglass. JB weld doesn't work too well.
If 100% gas is available in your area, try not to run E10. I tend to think the alcohol is what ate through the fiberglass. Gasoline doesn't seem to phase it. I've heard E10 was what was eating up fiberglass gas tanks out of boats.
Also alcohol is bad about absorbing water which will only cause it to rust worse.
Eventually you will most likely have to replace the tank. But the question is, can it be removed? It looks like they are part of the frame!