Hi Waterboy,
It would be helpful to know whether the affected wall is part of the boundary of your apartment, or is internal to your lot?
Waterproofing in a shower is not reliant upon the tiles and grout, it is the membrane underneath that does the work.
If the problem is in a common property wall, notwithstanding your obligation to maintain tiles and grout, it would be for the owners corporation to repair defective waterproofing. Your costs for repairing the carpet and skirting would be claimable from the owners corporation. Hence the question about the location of the leaky wall.
Likewise with the adjacent balcony, it is the membrane beneath the tiles which does the work of waterproofing and replacing sealant on a joint may work but will likely need re-doing when the sealant deteriorates. You may indeed have water ingress from 2 sources, the adjacent balcony and your shower.
You should address your concerns to the Secretary of the owners corporation and the strata managing agent. The owners corporation remains responsible for the waterproofing to common property even though the builder has gone, and you have only 2 years to claim for new damage to carpets and skirting.