I used 3m windshield sealant in the caulk tube when installing my gasket and window. I put it in the channel groove and put the gasket on the car first and taped it in place. Then I put it in the window channel and put in the window. It would probably be ok without it, but I didn’t want to remove the large rear window in the case that it did leak. The caulk is black, same color as the seal, and if you mask off the area around the gasket, chances are that you will come out with a clean install.
