My theory is they rebated it to aid locating it but then changed their minds. I don't think the rebate helps, it can pull the top back if the screw is tightened too hard and crack the drive inside the camcover. I have a friend looking into making me some tacho drives in another metal to stop it breaking so easily. He has his own CNC machine and likes a challenge. The stumbling block is how much it would cost to make, we'll see.