Sounds like you have a well worn in MK I there Mike. All the early models were stamped with Seattle, Wa because that was the location of the company's office. When the office was moved to Bellevue, then the stamp was changed to say Bellevue, Wa. It would not be totally unusual for an I52xx to have a two piece barrel since the company would revert back to those whenever the supply of the newer one piece stainless barrels came up short. Neither would it be unusual for the piece to rattle when you shake it. If that baby shoots reliably, then $300 was a pretty good deal. Because of the two-piece barrel, I would recommend that you "carry it much, but shoot it little", since those barrels have been known to separate sometimes.
Hope this helps, ...Deeton