Death wobble is one of the many joys of coil sprung Landys. Most often it is due to bad panhard rod bushings and improper swivel pin tension, but can be the result of a combination of things like worn dampers, weird tyre wear, a worn out steering box and bad ball joints. When mine went south, it turned out to be a combo of problems.
Check the panhard bushes for play. There should be none. Give your cross rod and drag link a shake to see if there is any slop in any of the ball joints, or have somebody give the wheel some back and forth action while you are under the beast and and look and listen for play. With the front of the car on stands, check for play in your wheel bearings and swivel. Grab the tyre at 9 oclock and 3 oclock and see if you can feel play when you give it a back and forth. Then grab it at 12 and 6 and give it a shake. If you feel slop in both positions then you have wheel bearing issues, but if you feel slop at the top and bottom the you most likely have swivel pin issues. To fix that you need to remove some shims on the upper swivel pins (if there are any left).
A steering damper replacement alone will not solve the problem if you have the other problems.