Peter – DaveB is correct, in that the Owners Corporation (O/C) is responsible for the removal of tiles on the common wall, waterproofing that area to current standards (to a height of 1.8m I think), re-tiling to as close as possible match the existing tiles, and only if the bath is against that wall, if it’s drainage is not leaking, and it must be removed in order for the above works to be done, then the O/C is also responsible for that removal and replacement.
If the drainage between the bath and the floor is leaking, then the Lot Owner and not the O/C is responsible for the removal and replacement of the bath if that’s required to make the repairs.
It’s worth noting that in NSW, all waterproofing in “wet areas” must be undertaken by a person who holds a specific Waterproofers’ Licence, and they must provide the Lot Owner and the O/C with a Statement of Compliance with AS3740 upon completion of the work.