In research before buying, I asked a hobie rental agent what goes wrong. He told me that the pontoons older hobies are not supposed to be stepped on. Once they go soft he cuts a hole in the deck and adds wood stiffeners glassed in to shore up the deck. If not done, the pontoon will buckle and break in heavy speeds.

Glassing is just messy... but once you get it down, just about anything can be fixed.