Bad fuel??? So the dealer says?

I have an 06 C230 with 37K miles on it. Never had big issues with it until recently. The car started idling really really rough... and lost all of its power... it was really undrivable. Called the dealership service dpt. to set up an appointment. First thing they told me was a bad MAF, but they had to order the part from "Germany" they kept my car for about a week while waiting for the part. In the mean time they told me that they had found a problem with fuel injector #6, so they replaced it.

The day I got my car back, as soon as I got on the freeway and got on it, it started doing doing the same thing, so I took it back. After a few more days they told me that I had gotten "bad fuel" in the car, and after taking 3 fuel samples the 3rd one came with particles of rust in it, that were too fine for the fuel filter to catch, so it was clogging my fuel injectors. They quoted me a $1200 job not covered under warranty to clean up the tank the fuel lines and the injectors.

I got the car with me now, I didn't let them do the job on it beacuse I wasn't too sure about that being the real problem. They car has been driving fine for about a week, but I'm driving it very slowly not getting on the gas at all. Any ideas... Please help!