now ive never done this on a healthy specimen but have save a number that were rescues from petshops that had RTN i would just cut about a half inch into good flesh from the RTN either splitting in half or just cutting rotten part away the used jell superglue and sealed of exposed side almost making a new skeloton of sorts has worked everytime so should do the same on healthy coral.I just did above mentioned on a hammer ill post pic of what i did ,lights off right now so ill post tommrow.