It's on the upper rt. arm of the perforated "X" of the scissors of the actuator. An aluminum alloy piece held on to the arm with an anti-rotational bolt. To adjust, loosen bolt, it slides on a diagonal, sort of, and sets a lower "stop", to prevent too much downward movement of window. Check side channels to make sure the veloury stuff isn't too crudded up in the channel itself; perhaps a little white lithium grease on metal sliding/pivot points.
The Golden Rule
1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)