1) It would be a good idea to get the codes read at an independent european/Mercedes shop. Just get the BAS/ESP codes read, nothing more. Maybe that would help in narrowing the problem to something more specific. Be sure they write them down exactly, so you can reference in the future should that become necessary.
2) Open the connector and using "DeoxIT D5" contact cleaner give it a good blast. Deoxit is both a cleaner and a lubricant. It will help cleans the contacts of corrosion. For about $15 -20 a can it is worth a try. You might also try a conductive grease BUT VERY CAREFUL NOT TO PUT SO MUCH ON IT COULD ARC ACROSS INDIVIDUAL PINS!!! I have a silicone base carbon black grease with micro bites of copper suspended in it which I tend to use on any connector I take apart and can get to the pins easily.