Polyurethane bushes in Shocks is a joke.

Rough corrugated roads are torture for shocks as we all know, but what often gets overlooked is these polyurethane bushes in shock absorbers "they kill shocks" they rattle and shake the valves and do not give enough side to side freedom, for example on the rear of a Land Rover the top bush is under a lot of stress sideways and this causes the piston and rod to put more pressure on one side of the seals and bore and eventually lead to leakage.
The solution is to go back to good old rubber based bushes which have a lot more compliance and insulate the shock from unnessasary viabrations and movements.
Polyurethane is great anywhere else dont get me wrong. its just a bit of a wank and actually causes damage in shocks.

The smart suspension companies realised this some years ago, and some just have not learnt their lesson yet.