The passenger side mirror is loose. Could it be the spring? The drivers side mirror is solid. The top of the passenger mirror is okay. The mirror doesn't seem like it will off by itself. Definately no automatic car washers.

It's a power mirror, color matched silver.

2004 sedan

just had the same problem with mine, only i have a 1988 z24 so it could be different from yours.
for the mirror there are 3 screws ( you just move the mirror up and down, left and right and you can get to all of them). for the complete door mirror housing there are 3 bolts that you can get to from inside the car. open the door and remove the triangle interior piece right there were the mirror is mounted to the door. the 3 studs with nuts are in there.
but like i said yours is a different body style then mine so may be a little different. but i bet it is still put together the same way so it gives you a starting point

Once the mirror is off of the car there is still no way to get inside of it.

It has a big wrap around spring so if hit something spring gives instead of seriously breaking something. Over time the plastic piece that holds spring on breaks probably what happened.