2000 R Rear Window Water Leak

I have a water leak in the R rear window area of a 3 door ext cab Silverado.  Have used Silicone on the outside around the window molding, yet it continues to leak.  There is a rubber molding strip that extends forward on the roof and wonder if the water is coming in around there?  Has anyone experienced a similar leak and what have you done to solve the problem?  Much thanks for your help.