If the battery vent seals are broken, this is a result of pressurised gas («?
??»* in Greek, i.e. oxygen and hydrogen in perfect burning analogies, which explodes violently when ignited) escaping the battery compartments. This usually happens during overcharging, and the vent valves protect against explosion from the gaseous pressure being built within the sealed battery compartment.
In your case, I think that the extended short circuit overheated the plates, resulting in the vaporisation of some of the electrolyte and the permanent destruction of a part the battery plates coating material.
Anyway, if the electrolyte has lost water (in the form of escaped gasses) the battery needs to be replaced because the electrolyte acid concentration is not right anymore, directly affecting the battery capacity and life.
[ * ] Transliterated: "crotoun aerio" (since the forum software database does not seem to support Greek characters...)