side passenger window install question, rubber piece or urethane caulk? Options

[914 RZ-1]

I found the thread on installing the side windows (not the little triangular ones, but the big ones). They state to use urethane caulk (3M Windo-Weld # 08609) to attach them to the rail on the window mechanism. However, the factory install uses a rubber u-channel.

I'd rather use the u-channel, since it doesn't appear that using the caulk allows for any adjustment fore and aft after it cures.

My windows were taken out to paint the car so I have no reference for putting them back. The window install post stated to measure about 4-3/16" (106mm) from the front, but what is the tolerance? I'm thinking there could be some variance in location plus or minus 1/4" (6mm). I thought of setting the window in place, but I won't have the triangle window in, so there will be nothing to reference the location off of. Any ideas on solutions?

Where can I get the u-channel?

Also, is the u-channel glued in or just friction-fit?

[914 RZ-1]

Here's the rubber U-channel:


It is 2.5mm thick.

I found another one! It was stuck in the metal channel. The one I had was stuck on the window. I was able to carefully pry it out. I'm going to reuse both of them. They appear to have been secured with some caulk of some sort as there is still residue. I could rub most of it off with my fingers. I will obtain some butyl caulk and secure them with that.