If it’s the original bathroom then the waterproofing is the responsibility of the OC. No if’s buts or maybes.
You can get details of the insurance policy just by asking the strata manager or the secretary. It’s a document of the OC and hence you are entitled to it.
You can lodge the claim yourself , even if the strata manager tells you otherwise.
Strata insurance policies often include cover for owners fixtures and fittings, so your stuff may be claimable. Don’t expect to get replacement cost back as most policies take into account the depreciated value of fixtures and fittings.
Since the leakage is covered by insurance, the cost should not be an issue to the OC. The only cost to them is the excess.
In my opinion a way to ensure the repair is not done on the cheap is to let the insurance company find the tradesman and get it repaired by them. Since it is common property you have less say as to how it’s repaired.