Experts please, will I need to re-do the 2nd floor bathroom?

There is a leak from the 2nd floor bathroom to 1st floor ceiling. When i looked (from 1st floor) it appears that the hole cut for the main toilet pipe was misaligned so they concreted it up and moved the toilet pipe 1 foot to the right.

Now there is a small drip leak coming from a nail that sticks out of where they reconcreted (or patched) the 1st pipe hole they cut.

Is the leak seeping through grouting through the newer concrete patch? Or could it be a water feed to the toilet? And final question, just how much physical damage should i expect for this problem to be fixed?

Thanks in advance for any help and suggestions. Im starting to think the developer is a right cowboy and am beginning to regret buying our 1st house here.

Could be coming from almost anywhere.

Does the drip only happen after use of the upstairs bathroom? Showering? Toilet?

The correct fix would be to remove the nail and investigate the source (which could involve some serious floor digging), the Thai fix would be to remove the nail and fill the hole with silicon.

Good one Crossy good one. Unfortunately true.

Water truly can run a long way from the source to find its way down. You could try putting some toilet paper around the base of the toilet, flush a few times and see if the paper wicks up any moisture. Try the same around the shower base. Your rerouted toilet piping should be visible so probably not that.