For what its worth, a very knowlegeable poster on another forum had stumbled upon an FBI file that stated that Gerlando Sciascia was believed (by the Bonanno admin) to have ordered the murder of Cotroni's son and was killed himself as a result of it. I'm not sure, but I believe this was apparantly said by Massino himself.
Gerard Gallant, Rock Machine hitman on orders from Plescio, confessed to having killed Paul Cotroni. The Massino angle seems strange to me ,if you can get Massino's testimony on this matter I would be interested to know the connection.
I agree, maybe West End leader Raymond Desfossés had something to do with it because Gallant was his man.