Mercedes Forum - Mercedes Benz Enthusiast Forums - can anyone offer advice please

Hello, I'm fairly new to this but wondered if anyone has had a similar experience

I had a cam shaft sensor oil leak, on my SLK 200 reg late 03, Mercedes main dealer in Teesside undertook the repair and replaced the sensor, wiring loom harness etc etc

We discovered an oil leak coming from the sensor, (so much for the quality inspection before the workshop sign off on the work) the car was returned for repair, within 24 hours the engine management light was on the car was returned again for the harness to be cleaned as "oil had pooled there"
collected car yesterday drove it for half an hour and engine light back on car again returned to garage
Please can you give me any advice, is this a usual fault with this kind of problem? When I complained today that this is the third time the car has gone back I got the impression the Garage will try to say its an unrelated fault as they just seem unable to resolve this ......any advice you could offer would be so appreciated.

Thanks