The steering damper is a skinny shock absorber that goes from the idler arm pivot point to the drag link. When you look under your car, look for the left tie rod connected to the left wheel knuckle. I think the left tie rod is green while everything else down there is black. Follow the tie rod inward to the pitman arm connected to the steering box. Also attached to the pitman arm is the drag link that runs parallel to the engine cross member. About 1/3 of the way along the drag link from left to right is the mount of the steering damper.

You can't tell much by looking at it. You pretty much have to remove it to test it.

Sixto
91 300SE
81 300SD