Not hard but you need to make your own gasket for the bottom half of the oil pan.
Is there any chance your battery might be low? Prior to replacing my battery I got several warnings that my oil level sensor was defective. They went away as soon as I changed the battery. Other symptoms are unexplained loss of 'sync' on windows and sunroof and BAS/ASR messages. Any battery over 4 years is suspicious although some owners report 7-8 years.
I am looking to replacing the sensor myself. I have a 2006 c230 that I recently purchased with the constant on and off message of "check oil level at next gas station". Took it to the stealership and they confirmed that it was a sensor and they want upwards of 300 to replace it. I am trying to find the part myself and change it. This is my first mercedes,but I have worked on plenty of nissans,bmws, and mitsubitshis so I am not afraid to get my hands dirty. I am assuming that the sensor is attached to the oil pan just as the old c-class models? can anyone confirm. Also some helpful hints or tips would be much appreciated