I don't know that much about the O2 sensors themselves. The two things that I have heard that kill them are operation with leaded fuel and running the engine without the cable connected to the sensor (I believe because the heater is not operational). I guess they could get totally fouled by carbon as well. I recently swapped my sensor from one engine bank to the other, and it did have a lot of carbon on it (since under some conditions my engine still runs pretty darn rich), but not of the holes where clogged or anything. I just wiped the carbon off before re-installing it.
Did you pull your sensor and examine it? Does your system have any sort of power on check routine that occurs when first starting your engine?
