Welcome.
That is odd. Certainly not something regularly reported on here. Being it is a 10 year old car and well out of warranty I'd be tempted to run a bead of silicone around the seal inside and out if that is accessible. If you do this be careful to only use a small amount and don't get any on the door trim or seats. When it dries just trim any excess off with a razor or stanley knife blade.
I haven't got an FD hatch available to look at to see how the glass is put in, but if I did, I'd be inspecting the other side that doesn't leak and try and identify any differences.