I have never managed to patch up a leaking battery totally effectively. The things seem to be made of a plastic that nothing sticks to ( at least once it has been contaminated with acid). I have tried car bodge, araldite ( brand of epoxy) , fibreglass resin and glass tape etc and none have worked satisfactorily. The best luck I had was with flash banding for roofs. Not sure whether it exists outside the UK but it seems to be a plastic film backed with a bitumen based sticky layer. If you can clean off ALL the acid and press it on well and heat it slightly it will stick.

The old glass cells used to burst their jars when the positive bars expanded. That was pretty final unless you caught it within hours and re-housed it. At least you didn't have a conscience about trying to rescue it. Not sure how long you can prolong their life. As long as the positive link bars hold you may keep them going, others break the link bars and become useless before the capacity becomes too low to be useful.