300TD wagon, side window replacement problems

I am replacing the glass side rear window. My problem is in fitting the rubber seal into the "L" shaped frame that mounts to the vehicle. The glass itself fits into the rubber seal. The problem is in aligning and inserting the rubber seal into the "L" shaped frame. I have tried mild heat, glycerin, soapy water, at least five different brands of silicone spray, and finally electrical cable lube used in pulling wires through conduit. In every case I have used small flat tools in trying to work the seal into the "L: frame. Nothing has worked and this problem is driving me nutz!! Local auto glass places will not even touch the job, pleading inexperience and no desire to be responsible for breaking the replacement glass. Even the wise people over at Mercedes Shop dot com were not able to offer any help, which I think is a first. Certainly someone out here has done this job successfully and I would sure like to find out how they did it