Strata bunny – if it’s the original shower area (floor/walls) that was in place when the Building was constructed, then it’s the Owners Corporation’s problem and conversely, if the area’s been since renovated by an Owner (not necessarily you) then the problem’s yours.
Assuming the former, then you need to advise the Owners Corporation (that’s not some separate entity and rather is made up of all Owners by the way) in writing of all the relevant facts that you’ve mentioned in your post, and further advise that if the repairs for which it’s 100% responsible under the provisions of Sect 62 of the NSW Strata Schemes Management Act (SCMA) and for which it’s already admitted (some) responsibility are not commenced in say 7 days, then as it’s been 15 weeks since you first requested it to “exercise its functions under Sect 62” (use those words) that you’ll be seeking an Order in the NSW Civil & Administrative Tribunal under Sect 138 of the SCMA so as to have it immediately exercise those functions.
You’ll find some additional information about Mediation and how it fits into dispute resolution HERE.