Ok, the good old tyronsea in one of it's last graphics before the company went bust was made of simple ABS plastic heated in two parts in separate moulds then joined together with a glue and pumped full of 2 pack foam which can soak up water like a sponge.
We used to repair the thousands that we sold in the Eighties with epoxy after a bit of a sanding with 80# but I would definitely think that given the age that a Sikaflex would be the better option given that the ABS would be dry and brittle.....have fun and remember that I can lend you my electric chainsaw lol