Rear Passenger Side Leak

Hey guys, have posted about this before but it was a while ago and I have had a new development on this so I'm starting a new thread.

I have a water leak dripping down on my rear passenger seat, it is coming from the seal that goes around my rear window. It is consistently always in the same spot, the leak does not move.

My initial thought was to replace the third brake light seal thinking that may have been the cause - it was not. I'm now left wondering what it might be. The only other solution would be that the rear glass needs to be resealed?

If someone else can point me in a different direction it would be appreciated, otherwise I'm going to have to start getting quotes to have the rear glass resealed and I'm not looking forward to how much that may cost (I have no idea how much something like that costs).

Thanks guys.