ok, you have the arm of the regulator that connects to the greased track on the bottom of the window...well,the white plastic piece is what connects them together...the white piece slides back and forth in the track as you lift and lower the window...

__________________
1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction