If you place a voltmeter in series along the sensor's signal wire, you should see the output voltage oscillate between 0.4V and 0.8V (for RB26). If it is outside that range, doesn't oscillate at all, or the mean is not around 0.6V, then the sensor has had it.
If you have access to a Consult cable, that is 1000 times easier, as you need to check the sensor when hot (ie. scorch your hands trying to place the meter along the wire).
Hope that helps. If you're near Western Sydney I can help out with the Consult cable. Cheers.