Loose passenger-side miror on W124

[Hydronuclear]

Hey all, I just bought an 87 300e and noticed that the passenger side mirror can't be adjusted (even though I hear the power window motor working). The housing is firmly attached to the body, but the mirror flutters around (back and forth) when I'm on the highway. Yesterday, I lifted an edge up to see what might be out of place and noticed a crossbar on the backside of the mirror. Is this supposed to mate with the crossbars in the housing? I didn't want to push too hard and break the glass. Anybody run into a similar problem? Thanks!