I believe mine is 'working' because it passed the emission tests.
However, after going through all the original owners receipts, I'm starting to believe my 560 is equiped with the original sensor. The car has 158,000 miles on it.
From what I've read and what you are saying Paul, it sounds like not all 'working' sensors are created equal and that if I were to replcae my 'working' sensor I might very well achieve better performance.
What are your thoughts?
....and thanks again to all for your input.