Hi
If you are interested in getting someone who really knows Mercedes, will do what is necessary and will not rip you off then you can do no better than using the services of Andy Gayle.
The only downside is - he is in the West Midlands (Brum).
Have a look here
linky . There is a link in the thread to his website. He is most highly regarded.
It really is worth the miles , book an appointment have a leisurely drive up and have the day out in Brum - there is lots to do - he will even get one of his chaps to run you into town. It is only a 300 odd mile round trip ( a tank of fuel) - the Americans drive that far for a hooters bar - or so I am led to believe.
You will have no regrets - and yo will get your car sorted without the flim flam you have experienced from the tosser who told you the rings have gone.
There may be nearer specialist independents but AndyG is the best.
Do it - you now it makes sense.
Regards
NormanB