@thrillcat,

To prop the glass, use a short piece of wood and towel. Or a screwdriver or whatever you find appropriate.

@Ricky,

Re slider fix. Since I already buttoned everything up and am in no mood to open this thing up again, this is my thinking.
- I hate to buy the slider clips for $14/pair or $28 for both front doors and have them sit on the garage shelf for months and years, waiting for the stock parts to fail, when I can...
- carry a roll of Scotch Tape (Packing Tape) in the trunk for emergency repair. Should the glass drop down (when the slider fails), I can always raise the glass by hand and tape it shut using the Scotch tape. Been there done that with my E39 LOL!!! Only then I will buy the slider clips.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT