I should mention that in the end, I ended up using W210 rear window regulators on the W123 Sedan (customer's car). Was a little bit difficult adapting the "sliding jaw" to hold onto the W123 window glass, and I needed to drill a few holes, as well as converting the W210 "smart" window motor (Pinch control) over to a non-pinch control motor.

Then I just very carefully aligned the regulator (tight fit) and riveted it into place. It's been working great for several months now. The best part?? It only cost about $20!!

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles