I think that the manual regulator spring might work here. Also, I had a very loose pivot point between the motor bracket and gear piece similar to the OP. On mine, that has a spring, some regulators don't have a spring, there is a flat section on the pivot point the spring rests on. I supported the center pin from underneath and use a hammer and punch to drive the flat section, that looks like a washer, down to tighten up the pivot. It is much tighter now. I didn't want to hit it more than necessary to remove the looseness and didn't want the pivot point to be too tight, bind and have much rotational resistance by having the two pieces be tight against each other. My friend has a parts car with manual regulators. I'm going to shag one and put it on mine since mine is also missing. Years ago, I upgraded my manuals to electric and I may have got the regulators from different G Body cars a the wrecking yard. I just noticed recently while troubleshooting my window operation that one had a spring and the other didn't. I think the spring will help when closing the window due to the spring. I think the spring winds up when the window is rolled down. I can see this as being needed on manual windows. Seems like some electric g body cars had springs, others didn't. Maybe it's on the earlier cars, I don't know.
