as we know the Tattaglias and Sol saw through Luca's ruse. I have no clue how it would be the least bit plausible for Sonny to go to them and pretend he had differences with his father over the drug business. All this would have done was send a message to Barzini that the Corleones were not only weak, but that they were divided within the family. Talk about the Don Slippin....