Thats a good point! I wasnt worried about making a mess because the car is mostly disassembled. I used the wd40 can with the smart straw. Peel the gasket away a bit and squirt. Move a little bit to the side and repeat. All the way around the glass. Inside and out. Didnt really get any on the headliner but it did get all over the package tray area and in the trunk, so that would be a bad thing to get wd40 all over areas that are gonna get painted or need to stay clean.