I am a "youngfeller", I guess. I have only had my MK II since October. But I do have a possible reason for your problem. If your gun was "barely used," it might not be broken in yet. I was told by members of this forum not to worry about any feeding/extraction/firing problems until I had a brick or two of high velocity (breaks the gun in better) ammo through my gun. For me it only took a box or two until I stopped having any trouble that wasn't caused by the ammo.
If you get some more rounds through your gun and are still having trouble, and you are sure it isn't a cleaning issue or something, you should give Ruger a call. Their customer service is excellent, and used or not, they would probably let you sent it to them to be tuned up for no charge.