The play in the glass is pretty normal. It doesn't help matters, but it has more to do with the weatherstripping being worn out. There is a single bolt that attatches the window to the slider, so there is going to be some play. I really don't think there is technically a stop. The bracket that holds the window does bottom out on the bracket attatching the track to the door. So it does stop, but nothing tells the motor to quit applying power. SO if you roll your window down and keep pushing the button after it is down, something is eventually going to give. THe somewhat grinding sound is the motor gear slipping on the "track". So like I said, you could theroretically put a stop in there at a higher point to keep the window from reaching the worn part. I just had one apart and should have taken pictures, but I didn't. I have another to do so I will try to postpics. If you get it apart, you will wonder why it lasted as long as it did.
Dustin