Quarter window gaskets not quite like originals

Just rebuilt my quarter windows on my 74 Duster and am finding that the new gasket doesn't want to seal tight against the body at the bottom edge. I measured the old gasket, and it appears to be wider than the new one. The fit was good in the frame but I'm sure water will get behind it and make its way down into the body cavity. Don't want to fill the gap with silicone. Bought a seal kit from Partsmix that has some of the other perimeter foam tape seal. They tell you to tuck the white foam strips in the kit under the flap of the gasket to help it seal against the quarter, but it won't even fit behind the new gasket. Considering cleaning up my old gaskets and reinstalling them, but then I will have a new set of useless gaskets. Finding out there is nothing like original equipment.