The original material made by GM looked like the first image below. I know this because I used to buy it directly from GM until I couldn't get it any longer. Since GM dropped this product (early 80s), it has only been made by others and it looks like the second image below. Please study this and you'll see it reveals some things. You will see there is no arch on the bulb side at all. For this to seal, the arch must be present on both sides of the retainer. The non-bulb part of the arch is present and the extruder wanted that part to be sincerely arched. The thickness of the lip tells you that clearly. The second part of the arch (on the bulb side) presses the bulb toward the outside of the cab and against the door (where it will contact the door but only slightly). The original material over time shrunk and got more brittle. You don't want this to press too tightly against the door. It was never intended to do that. If it pushes too hard against the door, I can promise you the door will become very hard if not impossible to close. A one inch piece of this makes it seem very easy to move the bulb back and forth. With 5 feet of it bent into a U, the bulb becomes exponentially harder to move, so as I said you want it to just kiss the door a bit. Good luck!
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
