It doesn't matter if there's no money in the sinking fund, the Owners Corp has an absolute responsibility, without limit, to maintain and repair common property. That means if they don't have the money, they have to raise it – their finances certainly aren't your problem.
Also, your landlord has responsibilities to provide accommodation to a reasonable standard and this is something the landlord should have been chasing from the moment he or she was first notified of the problem.
Now, you can either tell the landlord this, or take action via Fair Trading to force the landlord to force the Owners Corp to fulfill their legal obligations. Meanwhile you should also ask for a rent reduction backdated to the time when you first notified them that there was a problem.
Maybe explaining that this is an option may be enough to get them to do something about it. But you do have grounds for asking for an early release from your tenancy agreement.
Go to tenants.org.au and have a look at some of the fact sheets there – they'll tell you everything you need to know.