Well, of course copper spades will have to be periodically cleaned and the connections retightened, that goes without saying and I doubt that a really gas tight junction can be made down to a molecular level and yes, metal migration is indeed a problem. Bad connections are audible. I can clearly hear improvement, especially in the highs, whenever the spirit comes over me and I clean them all. When sibilants become sssibilants, that is genereally the signal for me to gnash my teeth and rend my cloths first and then get going.