I wouldn't just assume the sensor is bad...if it is coming on every 500 mi and you add a quart of oil and it comes on again 500 later it probably means you are leaking/consuming oil. Check your oil level on a regular basis to see for sure (check with hot or cold oil, but make sure you do it the same every time. If hot, wait for 5 min after shut down).
I had this problem recently -- turned out to be the oil separator, but could also be oil filter housing gasket or valve cover gasket.
The oil should be between the two notches in the dipstick.