The W 126 was build in Sindelfingen.

Check the VIN Number.

If it has a "A" in the middle, it was the plant in Sindelfingen

"F" stands for Bremen. "E" for Rastatt.

The engines at that time came from Untertürkheim, the rear axle from Esslingen-Mettingen, the gearbox very likely from Hedelfingen.

Kind regards
Eberhard