1999 Silverado Rear Window Leaking

I have a 1999 Silverado with a sliding rear window. The window is leaking. I tried running a bead of silicone between the frame and the roof and it's leaking as much as ever. Didn't even slow it down. I cannot seem to figure out exactly where it's coming in. Any ideas where I should look?

Looking at it from the inside it is definately coming in around the frame somehow.