I have come into possession of an old Gamo "Modelo Target" air gun that used to be my father's cousin's gun, probably from the early 1970's. I'm trying to find out more about it, especially how to maintain it aside from the minimal information given in the manual (put a couple of drops of oil on the exposed moving parts). I would like to clean the barrel at least. Also, I have noticed the gun shoots far to the left, and I have to crank the rear sight nearly all the way over to make it shoot straight. And it occasionally sends random fliers way off target. Is this just the nature of this gun, or is there some maintenance that can be done to help it? It's been sitting essentially unused in a closet for 40 years. I have a few pictures of it, but I am new to this forum and I can't quite see how to post photos.