2018 Tahoe Liftgate glass window

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Question:   Is the 2018 Tahoe lift glass designed to be open during driving?  I looked at the owners manual and can't find anything about driving with it open or not.

 

I just purchased a used 2018 Premium with 35000 miles and during a 10 minute ride the lift glass fell off the 4 hinge pins and down across the opening.  I push it back in place while struggling with the pistons and I now see the air dampener is not lined up properly.   This window was serviced at the dealership before delivery because the previous owner damaged it.

 

I only saw thin metal round retainers in place when I first took possession last month but now those retainers are gone!

 

So, has anyone seen...in writing....that the rear lift glass CANNOT be open during driving?

 

Thanks.