Violent front end shimmy at highway speed is a classic steering damper failure symptom. It's easy to check and easy to change. Disconnect one end and see if it offers resistance. If not, it's dead and needs to be replaced.

If there is evidence of oil leakage you don't even have to check resisitance. It's dead.

I've had to replace the steering damper on my '88 190E2.6 twice in 25 years and it's only got 82K miles, so it's as much a time function as it is a mileage function.

The steering damper is a high pressure deCarbon design like the suspension shocks. They don't degrade slowly like conventional dampers, but usually fail suddenly.

If the seal develops a leak and the pressure is lost, it's instant damper death and instant shimmy.

Duke