I'm the other one - My tank failed on the mount weld - fuel tanks & oil tanks can be re-welded but obviously they must be drained vented flushed dried & vented again prior to welding. - Morgan took care of mine as the car was still under warranty but there are specialist who can carry out these sort of welding tasks and it is specialist work.
Chris is absolutely correct about the bonding of the ply but you may not need a new tank - Morgan direct is probably the best option as they've seen a number of these issues.
