I have 114K on my 2001 E320. I have performed most 100K recommended maintenance with the exception of the oxygen sensors. My gas mileage is still ok based on on traffic conditions and my driving habits. Should I install new 0xygen sensors as a proactive measure or wait for it to throw codes? Also, I am still on original cats. I wonder if changing the sensors would help cats last longer. Also, perhaps gas savings may justify the investment? It costs approx $575 for all for sensors. Any advice appreciated.