Mercedes Benz C Class bouncing at rear

Rear suspension accumulators knackered ?

Here is an explanation of what happens with them ,

" Here's what happens when the ride go rough as yours is. 1st a word on how the shocks work. The damper valves are just normal as in a regular shock, but the shaft is quite fat compared to a regular rear shock. Now, think about if you had a dowel inside a soda straw... If you blew on the end of the straw it would push the dowel out...
Ok that is what the level system does. The pump pushes fluid on the end of that fat shaft & pushes the shaft down making the shock extend, thereby raising the rear of the car. Of course the fluid pressure is quite great.
Now, finally to the spheres (also know as pressure resivors). As the car goes over bumps the shock shaft moves up/down. The fluid inside the shock gets displaced & must go somewhere. That where is the pressure spheres. Inside the sphere is a very sturdy rubber diaphram with nitrogen gas behind it. Actually, the entire sphere will be full of nitrogen on a new one. As the fluid is dispaced it goes into the sphere & compresses the nitrogen. The compressed nitrogen does act as a spring somewhat. Mostly it allows the fluid to be stored durning compression over bumps.
Over time nitrogen excapes & the sphere fills with fluid. now you have a hydrualic lock situation when the shock needs to compress.
That is what causes the "jolt" you feel. Over time the sphere can completely fill with fluid & the car will jolt violently & can even cause loss of control.
This is why you may need to add a bit of fluid over time even though there is no leaks. I've changed dozens of these & it always cures the problem.
The factory way of testing these in put on a pressure gauge & start the car. There will be a pressure spike at a certain point & that is the remaining gas level.
However when you feel the jolt it is a sure sign they are bad. "

Thanks whittingehame for the info, greatly received. Do you think that its an expensive fix.

Usually a simple , minor job to carry out and parts are relatively cheap for a Merc .If you can get an independant Merc specialist , cheaper still .Here is a sample of the price you can get the parts for ,

http://www.partsformercedes-benz.com/product_info.php?products_id=3168