I feel like I'm going a little crazy. I recently bought the car in the title with a non-working rear passenger window. No biggie.

I changed the regulator which was all bent up and jammed, but while I was in there I discovered that the rail the window sits in is almost completely rusted through. It is not the following part:

https://www.amazon.com/Mercedes-w123-Window-Regulator-GENUINE/dp/B00AKR41GM

But the one that fits into the two tab slots on each end.

I can't seem to find a reference to this exact part and it doesn't make sense. There is a rubber piece that also fits around the bottom of the window and then into the rail.

Has my window been mickey moused or have I not been searching the internet correctly for this part?

Any help will be much appreciated. Thanks!