Boo, sorey to hear the bad news Doesn't matter which one is leaking best to do the pair and get the heads measured &skimmed accordingly, i'd also see if there's any little bits you wnat to do while it's apart, checking the valves etc, new plugs if they are due a change in the next year, i'd buy new bolts but that's just me,
Sure someone who speaks more sense than me will come along in a bit