Re: What material is the fuel tank of a late 80's
 

Mine are aluminum. I had a leak. Fixed it with Marine Tex. No good. Cleaned that off and used JBweld. Worked great. A year later it's still good.
For plastic...I dunno. Maybe somekind of hot glue gun or if ya rough the surface up enuff MAYBE the JB will bond to the plastic. ???

Re: What material is the fuel tank of a late 80's
 

If you need to repair the plastic, be very careful. This ethanol gas eats up polyurethane, so whatever you use, make sure the gas won't deteriorate it...