ok, it sounds like you'll have to remove the pulley thats in the way if it bolts onto the accessory it mounts to, otherwise you'll have to dismount the accessory.
the liquid on there needs to be identified, as it may be a sign of another problem you don't know about. or maybe you want to tell the new owner that you believe that sensor to be having issues but you didn't have time to get to it. where i come from, thats just as honest/doing the right thing as having it fixed beforehand. its only the guys who hide problems who i count as dishonest.
possibly it just needs to be cleaned so it can get an accurate reading again