But if you have a water ingress problem, and you have reasonable evidence about it, it is the Owners Corporation’s responsibility to investigate and fix it. They should arrange an engineer or expert to investigate and report.
There are a lot of ifs and buts in the above response but the line quoted here is key. If common property is causing a problem, then the OC must pay to fix it. If they want you to arrange an engineers report, you have to make it clear to the committee that the OC will have to pay for it, ultimately. Take it as a positive – they are going to allow you to choose your preferred engineer – and they will pay, whether they want to or not.