I looked here and at the Hobiepage recently: please Use EPOXY resin for injection into multiple holes, do not use polyester resin. I have fixed several of these- usually with impact/physical damage that came out ok.

Again- usually this is the sad result of neglect- leaving cats built of fiberglass/polyester resin/foam sandwich uncovered in the hot sun & full of water- its a mean trick. When in unrecoverably bad condition, the inner glass layer has come totally loose and is hanging down: The foam has turned to sawdust-like crumbles. Sorry but Botox won't help anymore