You will need to pull back the seal with your fingers enough to inspect the entire length of it on the interior side of the seal and find where it has been staked. I had three stakes on one side (spread out along the length) and two on the other (both near the end of the seal). So I assume they can be anywhere and have a indeterminate number of them. You will need to undo the staking enough so that the seal will be able to slide along the C channel. I don't have any photos of this part, but I took a wide blade screw driver and inserted it into the channel and dug and pried enough to allow the seal to slide. You may really have to dig in there to get enough of a bite to undo the staking. While my seal is of average shape, the inside part of this seemed to be the most flexible and sturdy part of the entire seal and I was able to really dig around at the channel without damaging the seal. I suspect this is because this part of the seal is typically hidden away from damaging UV light, etc. by the interior trim.
I don't know how cheap or easily available a replacement is for this aluminum channel. If it is cheap, I would not worry about what you do to it to get it to the point that the seal will freely slide. I haven't tried it yet, but I suspect that if you don't mangle it much, that you can bend it back and reused it. The part you bend should be hidden by the trim once reinstalled.
Click to view attachmentTo help get the seal to slide, you will to lubricate it. I used a child's medicine syringe (available at a pharmacy or grocery store) and soapy water. I used regular glycerin dish soap and just a small bit of water. Whatever lubricant you use, it should be water based and not petroleum based (such as mineral oil).
Click to view attachmentYou should see if you can wiggle the seal a bit in and out (perpendicular to the channel) to see if you can loosen it up a bit where it might be stuck to the channel. Then you can try to use the syringe to squirt the soapy water in. If you get it in just the right place up near the top, you should be able to get a stream to run the entire length of the seal and drain out the bottom. Keep at it until you feel you have the soapy water between the seal and the channel along the entire length. It should run freely once it is loosed up.
After you have it lubricated, you may need to wiggle the intersection area between the top and side a bit to break it free from the frame as well. Be very careful as this is a very fragile area on the entire seal. At this point, you can start to try to slide the seal.
There are a few key things to remember at this point...
(1) Do not whatsoever try to pull the seal by grabbing a hold of the area around the intersection of the top and side piece. These pieces have been extruded and/or molded separately and then connected during the manufacturing process. They are weak where they have been joined together.
(2) Start pushing from the bottom, but then work your way up along the entire length by applying pressure on the seal in the direction that you want it to move. Wiggle as you go and apply additional lubrication as needed. Keep repeating this motion and if all is good, it should start to move.
(3) If it is not sliding something is wrong. Check to make sure you have undone the "staking" enough and that you can wiggle the seal along its length. If it is lubricated enough and has broken free, you should hear and see the soapy water squish out of the channel all along its length.