This was a bugger to find, daughters new car water leaking down left pillar soaking the boot and going into the wheel well, 4 days to pin point it. I had half the rear of the car stripped down , headliner half off ,hatch completely off inside panels off backseat out ,I could see where it was coming out down the pillar but couldn't tell where it was coming from, no plan B. I ended up getting some good tape and made reservoirs around all the wire plugs and around the hinges ,filled them up one at a time and found the left hinge was the culprit. It wasn't leaking from where the hinge connects to the body but was leaking from where the bolt goes through the hinge. I purchased a new hinge and found the bolt was part of the hinge, got some good sikaflex, (don't use silicon, it will rust it faster than water ) gave it a paint and no water, you could go over the bolt with sikaflex to stop it but I may look a bit messy.
I hope this helps someone.
