I've used epoxy resin, which is fine as long as you securely tape the bottom to stop it slowly flowing out again. But I've also used that 2 part stuff which is sold for mending dents in car bodywork (the stuff that you smear on, let it set, then sand down) which also worked perfectly.
Drysuit inflators come apart easily; the button and spring are usually retained with a circlip that can be prised off with standard caving hostel tools e.g. a couple of forks). They have plastic housings which wear in gritty sumps and eventually allow air to dribble into the suit. The only remedy is a new replacement. Try asking around folk who have been cave diving for a lot of years; they often have one or two marginal ones in the spares box. Or go to any dive shop which does maintenance work on drysuits and they often have something kicking about which you might be able to scrounge.