Help needed with plastic gas tank fix.

I just picked up a 91 KDX250. The gas tank has been botched up where there is a brass insert for attachment of the side panel. Bolt was sheared off then insert partially drilled out. Now it leaks gas around this. I can't seem to remove the brass insert. Anyone have suggestions as to what to seal this up with that is a good gas resistant fix. I'd like to use a hard compound that I could drill and tap for the side plate screw if possible. Help much appreciated.