I know from experience that leash agression is more them feeling in a way that the other dog is invading their terratory, and you are part of it so they must protect you.
With the non altered dog agreesion I'm not sure what goes through their heads, my boxer is like that too. Fine with young pups that haven't matured and are not altered but adults are a whole different story if the dog is his size. I had a female dog that was like that too, she could not stand unaltered females.
This is something that is common to a lot of dogs and not a real breed specific issue.
One question I do ask is to please try and describe how he acts in detail, because there is HUGE difference between aggression and dominance