Gunk On The Inside Of Both Driver And Passenger Windows

[provines]

About eight months ago, my driver side window stuck. I took it in and the dealer said it was tree sap, cleaned the window and all was well. It did it again this weekend. Taking a close look at both the driver and passenger side, I found a line of black gunk that appears to come from the window seal on the inside only of the window. If it were tree sap, I'd think it'd be on the outside. The dealer insited on charging me $45.00 to look at it since it was out of warranty. But, I reported this problem eight months ago! No go. I'm looking for documentation that this is a seal problem so I can throw this back at the dealer. I'm not paying him to clean the window. :censor: Any help out there? -Thanks