If there are no leaks, it`s probably the shocks. They are exspensive.
Did you put the guys in the trunk and then start the car and hold it at 1500 rpm`s or more? It has to be done that way.
I would take it to an MB tech to at least diagnose the problem. Then you can decide if you want to fix it yourself or let him. At least you`ll know what the problem is and save some $ instead of throwing parts at it.