You’ve put yourselves in a very tricky position here, albeit by trying to do the right thing. Strictly speaking, you should have taken action to force the Owners Corp to fix or replace the windows and you have no legal basis that I can think of on which to refuse to pay your share of others’ improvements.
Personally, I’d be tempted to run a case through Fair Trading to demand that the OC pays for your repairs. Your claim should be based on it being an emergency and they were negligent in their legal duty to maintain and repair common property. If you have evidence that you made many requests that were ignored, so much the better.
I’m not saying you will win but somewhere in the mediation you might get some sort of allowance made for the fact that you did the wrong thing for the right reason and they now want to do the right thing for the wrong reason.
If you are lucky, you might even get a ruling from the CTTT that the Owners Corp has to fix everyone’s windows but you don’t have to pay your share – it’s a long shot but the CTTT is a strange and illogical beast.