Hi KiwiPaul,
To answer your questions,
The building is 10-11years old, And yes it does leak every time it rains.
I believe this is a issue that has been going on for a while but the previous owners never disclosed this to us at time of purchase and did not show up in any strata reports, we bought the property in February this year.
I have come to this conclusion as when I pulled the carpet up there was plywood screwed to the concrete slab and the orange waterproof sheeting under that, The screws were all rusted and you could see water stains on the plywood. Also on the slab were glue marks from where they had previously had carpet down.
I feel we would have a case against the previous owners for not disclosing these issues to us.
cheers
sean