That is why I am replacing it
o2 sensors will change readings because there old .
I spent 30 plus years in maintenance in a large plant
And predictive maintenace always worked better than reactive maintenance
I wish the last owner took that approach to some items I had to replace
Also look at the bosch web sight and see the gas savings on replaceing old tired 60,000+mile o2 sensors
Besides why would bosch and Mercedes say to change it ,
if it were good ???
They now from experence that they are in the fail zone period.
I guess its pay me now or pay me later deal.
Some times we get away with it , but I am going to keep this car so might as well get the full time out of the sensor
By the way besides the connection and the $100 price difference they are the same o2 sensor. There both bosch sensors
Just that one fits the Mustang
Read old Posts on it.

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[B]Mike Y.
00 sl500 sport
88 560 sl (sold)