Plot hole: When Hawkeye and BJ buy Margaret a new ring, it takes a typo in the inscription to give them away - which makes both of them and Mr. Shin almost clairvoyant. Not only did they somehow guess Margaret's ring size, but Mr Shin - phew, Houdini and Uri Geller together don't hold a candle to this guy - actually somehow divined the exact type and font of the inscription in the original so perfectly that Margaret actually only spotted the difference from the missing 'n.'
Plot hole: In a tape home, Winchester implores his father to get him out of the MASH and suggests that Senator Griswold should help as his father "paid good money for him". As the length of time the show ran so exceeds the length of the war itself, inconsistencies for dates are perhaps unavoidable, and it might not be fair to call them mistakes. In this case however, the writers/producers have carelessly picked a senator who only served from November 1952, making dating inescapable. As Charles, in the same episode, complains how hot it is and everyone is in shirtsleeves, it must be very late spring, perhaps May, at best, just a month before the end of the war. To emphasize the mistake, by the next episode it is late fall/early winter.
Plot hole: In this episode, the military money, or scrip, is being called in and exchanged for a different color (and assumedly design - otherwise counterfeiters could just keep using their printing plates) to battle counterfeiting. However, in previous episodes several colors of scrip are being used equally and at the same time - e.g. in episode "Hey, Doc" (4-5), Sgt. Kimble collects a pot consisting of both blue and tan one-dollar scrip notes. No previous indication was given in the show that the army started a practice of using just one color at a time.