I'm replacing the faucets and associated isolation valves in my
bathroom vanity and have a general question. The valves are threaded
connections with brass ferrels and nuts. I cant figure out how to get
the existing ferrels and nuts off the copper pipe without cutting the
ferrel and I'm afraid of marring the pipe. Is there a risk of these
ferrels leaking if I hook them up to the new valves? They dont
currently leak but the valves are getting old and corroded.

thanks, dave