Just some info on sensors. Bosch were the inventor of the oxygen sensor and according to them they have a service life of 50-100,00kms depending on the type. There is the "Thimble" type sensors which typically have 1 or 2 wires from them or the "Planar" type which has 4 wires. The "Planar" type are the ones used on the T's etc I believe. They reach operating temperature 2 times faster than the thimble type which reduces cold start emissions by up to 50%. Exposure to heat, carbon, soot, gases, antifreeze, thermal & physical shock etc cause the problems. I guess if we are punching more ponies out it may have an effect on reducing the life of them. All this info is straight from Bosch.