Anybody who has a pre-facelift W210 probably has had a problem with the floppy mirror syndrome. A car wash or somebody whacks your side mirrors and all of a sudden they become limp. Well here's a fix, just short of replacing the assembly.
The spring in my hand is what gives the mirror its return. It's ridiculously beefy and because so, it causes an issue with the assembly.
Another pic of the spring.
Now this is what happens that causes the floppy syndrome. The bracket that holds the spring was bent back under the force of the spring and let the spring go. Without the spring, the mirror will flop around as nothing is holding it tight to the car.
Here's the bracket portion that I simply just broke off so I can do my fix. This housing is a bust anyway and there really is no way to reaffix the bracket.
So, how do you fix it? Stainless chicken wire. Grab the end of the spring with a screwdriver and pry against where the bracket used to be attached to tension the spring. Have your wire ready and tie it off. It won't break, the tensile strength of the wire is plenty.
That's all there is too it. The spring is ever slightly less tensioned that from the factory, but the springy-ness to the mirrors is back. No more floppy eared Merc.