ABS light is on all time. Drive shaft rings are turning ok. Tested front sensors, offside gives no reading on meter. Have not disturbed back sensors as i assume front due to steering lock normally break first. Is this sufficient to say its broken or do i need to have a diagnostic check. Also tried to remove it in case i have to change it, could not budge it, do you need to drill it out, or does the hub have to come off to drift it out. Is the sensor a main dealer part only ?