I've seen pictures from Europe of the side plastic panel replaced with OEM Mercedes glass.
https://www.furgovw.org/galeria/foto...o-Party-32.jpg
It looks like a lot of time and money, but is probably the cleanest "repair" that doesn't use the Westfalia panels. The water filler would have to be relocated, and I have no clue if there is anything mounted behind the steel window panel. I'm fairly certain that the biggest challenge would be removing all the metal shavings inside the van after cutting the opening. However, it definitely is a very factory look when completed.