ml320 1999 poor handling on rear

[turnerdv]

Hi I have a merc ml320 1999 with 71k I got a local garage to replace the rear shocks about six months ago with geniune mercedes ones and about two months ago when y went over a bump the back end jumps about to much and goes thud if this makes sense and its a bit twitchy driving down the road now. When you go round a corner it leans alot more then it did before as well. I have spoke to mercedes and they stated that they dont mind examing the rear shocks if i take them off (more expensive) but it would the first faulty set they have seen if thats the case. Any more ideas out there, any advice etc would be grateful.