1989 Chevy S10 Blazer Driver's Window Won't Stay Straight

The driver's side window glass on my 1989 Chevy S10 Blazer recently became "loose" and won't stay straight/vertical in the window channels. The
motor/regulator appears to be working fine with lots of torque to push the window up and down (I have to align the glass and keep it straight using my hands). There's a hole in the glass near the upper left edge.....is this supposed to hook into something to keep the window straight? I don't see/feel anything in the channel to attach to the glass.
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