replacing shut off valves
 

i have a couple shut off valves that are so corroded theyeither wont turn or hardly turn would it be ok just to replace the on and off section and leave the old ring and nut.i have half inch copper pipeing.what are the risked of breaking something and making it worse and is there some kind of goop that i can put on the threads in case washer is a little worn.im selling house and have already remodeled one bathroom but have inspecter coming over in a few days and just want to make sure things are ok.

If there the same sure you can. I've done this before, never gad a problem doing it this way.