All I can say is "Wow!". One of those little things that takes just 15 minute to replace and costs under $50. Bought one and just installed it.
The new one, in hand, is smooth and resistant to movement. The old one, one out of car, was easy to compress is short spurts then hit resistance as I could actually hear fluid moving. Then under pressure it would jump a little more, the more fluid sound. It was shot indeed!
Now the car goes down the road and no longer has an issue of wondering left to right. HUGE improvement. Also the steering is a little stiffer, but much smoother. The steering wheel feels as if it has more control over the actual steering - if that makes sense.
If you have an older dampener, replace it! I think I paid about $33 for a new Stabilus unit. Removal and installation on the W126 is self explanatory and very easy to due. Just be sure to use thread lock if you are using new or old locking nuts.