I did the exact same thing to my 240 except I went all the way around the hatch because the gasket seemed to fit perfectly between the ridge in the hatch, but I needed to make a cut where the arms of the hatch connect to the roofline. It definitely helped a little bit, but I still need to put in the other gasket around the rim of the hatch from a kia to make the rear hatch completely sealed and hopefully to fully keep all the fumes out. If you already have that piece in, installing this should at least help a little. If not check your rear lights. Sometime the fumes can sneak though there.