Good on your for going and reading the Aust Standards and calculating the ARI in relation to the problem in your complex. We had an issue with a storm water drain and I brought up the Aust Standards and Building Codes referring to storm water drainage, water runoff and roof plumbing and the ARI's but alas as I do not have the correct letters after my name it was not considered We did however get an engineer in to do a report, which stated basically what I had found for free.
I once worked in the building industry (in a support role – not a builder) and during that time read alot in regards to building codes and australian standards. I learnt that inproper storm water drainage or infact any bad drainage was one of the worst things that could happen to a building, not to mention expensive.
It costs about $500 to get an engineers report. Like Jimmy said, if your sinking fund can't find $2K plus a bit more, then they should start the special levies for any potential water damage to your complex. Water that goes under a slab is not good news – not just to the units directly affected, but to the hip pockets of all!