Thanks for the reply. I think I'm going to leave that window bottom edge piece alone. It may be a combination friction crimp and glue fit. The existing looks fine so I'd probably have to gorilla it out of there.
I guess we'll see what happens with the channel. Where i got it wasn't terribly expensive so if i have to redo it won't sink the project.

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6