I read there is some 3M weatherstrip adhesive you can buy, but at least in the first photo that rubber seal will have to be stretched a bit to make it fill out the full length of that crevice, all the way to the corner there. Since I'm still driving my old '03 ( ) the rubber is quite dry and not wanting to stretch a whole lot, at least for my fear that it will rip. I'm no expert (obviously) but is there a way, maybe something I can use on it, to soften it so it will stretch? Then after that what's the best way to set it properly?

 

I don’t know of any liquid that will undo 21 years of aging. I think what I would try is to stretch it slightly, hold it in place in some manner, and then apply the heat from a hair dryer. Then stretch it a bit more, again apply heat. Do this repeatedly until you get things lined up as you desire. Then use the adhesive, clamp well and follow the adhesive directions which might say allow 24 hours for full strength.

Having said all that have a source for a new piece if the original snaps.

 

Dang, that's a bit of an order. You can't buy these online or anything, can you? If so I'd rather just rip the whole thing off and try to apply a new strip.