Julian, I hear what your saying about it rotting out rubber seals and I know that can be an issue when someone slaps it about like they are icing a cake but when I use copper slip I put a very thin smear on the back of the pads and on the ends where its metal to metal contact. If the rubber seals were to come into contact with the grease then it would be such a small amount that its doubtful it would do much damage to the seals and even if there was, the damage would be picked up at the next service and rectified.