My 1989 had a bubble about the size of my hand. It was an easy fix with West Epoxy. Drilled several holes and pumped epoxy in using a syringe, starting at the bottom and going up taping holes as the cavity filled. Placed a strap over a piece of 2x6 lumber and around the rudder. Tightened it down snug careful not to deform the rudder. It seems to have maintained its shape and integrity.