Basically, the Owners Corp has a duty to maintain and repair common property. The tenant has certain rights under their tenancy and the landlord has rights and obligations too. All very complicated and fuzzy round the edges.
I don't think it's reasonable to tell a tenant that they have to put up with whatever inconvenience is required by the OC to achieve their ends. They have paid rent for an apartment with a working bathroom and that's what they are entitled to – or some sort of compensation if that is suddenly not available to them.
On the other hand, they should be prepared to compromise.
If they aren't I think the OC has to treat this an emergency – who knows what damage is being done to common property and other lots – and tell the tenant that they will pay for short-term accommodation for 72 hours while they fix the seal. If the tenant isn't prepared to do that, the OC will go to the CTTT and get an emergency order that allows them to go in, fix the showers then seal off the bathroom until such time as the sealant has set. The tenant can then do what they can to get compensation through Fair Trading.
You're right that the tenant can't be allowed to hold the rest of the building to ransom, but neither should they be deprived of services for which they have paid so that something can be fixed that is of no concern of theirs.