Once again thanks for the information. This is very interesting. After getting the price from Assenmacher ($88) I called the local (Cincinnati) Mercedes dealer and gave them the part number of the test gauge and they looked it up and said they could order one for $300+. After your last post about getting one from the dealer in Arlington I called them and they said they could order it for me and it would be $57 plus shipping which is fairly reasonable. You can imagine how excited I am about the fact that I may at some point have to walk in the door of the Cincinnati dealership!!