My dad bought an old Ruger Mk pistol at one of those storage unit auctions, and from what I can best discern, it's a MK I. The thing looks pretty damn ancient and the gun is pretty worn...worn so much that the serial number isn't really readable anymore. I can read the last 5 digits barely, but the first two are illegible. Should I worry about this as a potential legal problem? I'd like to send the gun into Ruger and have it serviced and repaired(it still shoots fine), but I am really hesitant as to getting nailed for this serial number issue. Thoughts?