Using abrasive inevitably produces grooves and, if these grooves pass across the seal mating surface, leakage will occur. Even a small dink in the valve seat will pass air. This applies to other sealing situations too, like copper compression fittings. If I need to clean the ends of copper pipe with wire wool, the cleaning is always done using a turning motion around the pipe circumference, so any grooves run around the pipe, and NEVER lengthways. The same applies to cleaning copper pipe for use in push fittings. When we moved to one property, we found the kitchen sink unit carcass was sodden and black, all because a slight dink in the mating surface of the outlet for the dishwasher water supply had caused a slow leak. The previous owners never noticed it.