Well, if you've been cleanin it regular and it's doin that, I'd send it back. It hurts to let go of your gun for a few weeks but Ruger will take care of it. You could break her down yourself, but you'd have to be savy with each and every piece. It sounds like a timing problem. Have you checked the coggs on the back of the cylinder for anything that don't look right? Is there a drag line etched in the last quarter inch of the cylinder? That's not uncommon, but can be a clue. It really sounds like something has gummed up the mechanism being that it does lock into full cock. If it is a bad part in the gun, I would leave it to the manufacturer, or if you don't have time to wait, a trusted gunsmith--but that may cost you.
Leo