At 58k miles I changed the 02 sensor on my E320 wagon. No check engine light came on, but it was getting suddenly 15mpg on the highway from normal 25-26. Ordering the MB part proved it was expensive, and worse, out of stock for 3 months. Went to Autozone and purchased the Bosch "Universal" for $60-70. Got the old one out of the dual exhaust pipe connectors with lots of WD40, vice grips, and warming up the engine while it was jacked up. Screwed the new one in, did the minor rewiring job, mpg is now back at 26 and the exhaust smells better.

My 1992 Range Rover has 189k miles on it with original sensors. No Check Engine light. Mpg is 12/15 city/ highway EPA. Actually now gets 10/15. Some last longer than others. Not running the right grade of gas can cause premature failure. Our 96 Explorer 4.0 V6 replaced an 02 sensor (tripped check engine and bad mpg at 80k) now needs the other one at 135k. Check engine has been on forever, who cares, mpg isn't suffering so bad. 1995 Range Rover 4.0 had 02 sensors replaced under recall in 2000.

I agree: 60k recommendation is probably for emission reasons.

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro