I haven't had this exact problem, but I put my Mk2 Navy Ka-Bar from a couple of broken ones. 1. Pop the pin out of the butt cap 2. Carefully remove all of the washers and separate them, make sure you keep them in the right order and facing the right direction. 3. Rub each washer with bear grease or some other heavy duty and thick leather preservative. 4. Stack everything back up. 5. Replace butt cap. This should work. If it doesn't consider adding another washer - just take a piece of leather, cut it roughly to size, put it in the washer lineup wherever you want, replace the butt cap. Take a piece of sandpaper to the new washer to get it down to the same size as the others.
Good luck. The old Mk 2's are great aren't they?
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"Gold is for the mistress, silver for the maid,
Copper for the craftsman, cunning at his trade.
Good! Said the baron, while sitting in his hall,
But Iron, Cold Iron, is master of them all." - Kipling