The window going halfway down has to do with the relationship of the short metal arm (that attaches here with a circlip) and the rest of the regulator when assembled in the car. Put it in, attach glass and operate the window- you'll see what I mean. The window regulator bottoms out on travel but the bar position will not allow the window all the way down.

The other things to play with/replace if they are worn are the grey plastic wedges with screws thru them- they need lube and are what makes the window travel smoothly and in correct relationship to the metal pivot bars.

The bend pictured above is effing critical to proper operation. If you are going to reinforce it, I'd suggest having both windows back in the car, assembled and operating correctly and then remove them for welding- it would be a MPITA to weld em and then find out the angle is off.

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95 E300D gave away
77 300D, 227k, station car
83 300CD 370k, body gone away to the rust gods, engine is in a Yota pickup, going strong
89 190E 2.6- 335k, no more
79 VW FI Bus- 154k summer driver
59 VW Beetle ragtop- 175k
12 VW Jetta- 250k
74 MG Midget-78k