Sensor failure is often heat related , when crank sensors first start to go out they often have an intermittent failure when the engine is at full operating temperature. You are cooling the sensor with water.
Mine went at 38,000 miles, seems to be a commonly replaced part.
you should never have to change your oxygen sensors. The only time you have to is if the PCM (powertrain control module) is not recieving any input from them. This would cause an MIL (engine light) to illuminate.
How often should you change the fuel filter?
When the computer throws the code that you need to change the sensor.
Every 50k miles
You'll need to take the harmonic balancer off and remove the timing cover to see it. Often you need to remove the timing belt to get it out.
as often as needed
You should change your oil every 3,000 miles. If you drive your car rough, then you should change it more often.
It has a chain with a cam gear and crank gear.
everyday
How often should you change water pump in a boat