I just called a local MB dealer to findout what it would cost to change the o2 sensor. I told him that I have 244K and never had it changed. He said that maybe it doesn't need it....bring it in for an estimate, it may be something else.
He suggested a cat. converter. I changed that 2 years ago.
As usual they want me to bring it in to give me a list of work that it needs.
So predictable.