The original window runs were one piece, molded to fit the door. The stuff sold by the meter is specifically for the coupe. You can get it from MB (expensive) or European aftermarket (surprisingly cheap).

It does appear that both versions are dimensionally identical, so the bulk material could be adapted. The cost would be enough for me to consider gambling on the aftermarket. I think you'd have to miter the ends though, as that stuff is too stiff and bulky to make the tight bends required for the front door. I don't know if it's available in true bulk length or just one-meter pieces. If the latter, it may take more than two one-meter pieces to fab a decent finished product.

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'79 240D