It's been caused by someone cross threading it at the start, trying to turn it in, then realising it wouldn't go in and having to take it out again. It will probably clean up good enough but best to replace it.
Coppaslip is not grease, it's an anti-sieze compound. As there is nothing to sieze on the back of a pad, it's not advisable to put it there as there is nothing to be gained.