Sounds like you are doing all the right things.
I don't know what the numbers are, but those sensors are neg resistance. You could try to test is by measuring the resistance, then boiling it and watch how the resistance changes. It should go steadily down. However, if it is intermittent, it would be harder to verify.
Also, since it is an oil temp sensor, it might be a cooling issue and the sensor is working properly.
Unfortunately, It could be other things also. Just to make life difficult.