Talk to the service manager. Ask for the name and phone number of your Zone Service Rep. Call 1-800-MBUSA, and begin correspondence with them concerning this problem.
It is very rare that the 722.6 fails at this high mileage. Usually, if it gets past, say 30-40K miles, the thing is bullet-proof. Pretty unlucky for you.
What year is your C230? Is it a 1997? That's the first year for the 722.6 model range wide, and there are a few updates to early build units. If they were not done, you may have a case that the dealer didn't do the required work.
Keep us posted.
1998 C230 "Black Betty"