I had major issues with my previous Nissan Note. Water came in via the mounts for the lights.for the last couple of weeks I noticed the carpet in the boot, was wet on the left side (facing from outside the jack side) I took the carpet out and dried it off and same thing happened again. couldn't see any issue with the grommet in rear tail gate as others have stated, but I did note the tail light on that side did not sit the same as the right hand side. To cut along story short, removed jack, and tail light cluster, and put back and the cluster definitely appears to have gone in further and now no more leaks.
hope this helps