After disassembling everything I found the lock cylinder (tumbler) was missing 2 of the 4 wafers. The rectangular end of the pot metal cylinder wasn't so rectangular anymore - a chunk was missing where it fits into the fiber contact piece. It worked but had some play when turning to mag.
I bought a replacement cylinder kit and after seeing how many flaws there were to fix before it could possibly work, I decided to fix the original.
JB Weld to the rescue! (that's cellophane tape creating a kind of mold for the JB Weld). Picked 2 of the new brass wafers (they're all the same) that came with the repo cylinder... ...filed them and got them to fit properly. The marks are to identify the order and positions. The wafers fall into the slot of the sleeve that surrounds the cylinder thereby locking it. The wafers raise up and unlock the cylinder from the metal sleeve when the key is inserted. (excerpted from Locksmithing 101
