Leaking Balcony due to Unapproved Renovations by Past Owners

Hi,  My parents have bought into an apartment that was renovated round 2002.  No body corporate approval was sought by the renovaters, nor has any approval come from the board.

The renovaters onsold the apartment to another party, and we have recently purchased from this second party.  Part of the renovations involved retiling a balcony, shifting the position of sliding doors and replacing these doors with bi-folds. 

It turns out that sometime around 2007 the balcony started leaking at the edge onto the balcony unit below.  Ostensibly, this was due to a blocked drain and water pooling because tiles had not been laid at a correct gradient by the renovaters. 

The owners that we purchased the apartment from have waterproofed the grouting surrounding the tiles, but no change to the gradient of the tiles has been effected. 

I understand from the head of the body corporate that no by-law for exclusive use of common property has been struck and applied to owners of the apartment. 

Are we responsible for costs of retiling and waterproofing?  

Or does the Body Corporate have to pay? How do we apportion the cost if it is shared responsibility? 

Can they block my application to have the renovations approved?