This article furnished by David Adams.

1. Fifty years of wear had caused the operating roller to wear the sides of the slot in which it runs, cant sideways and jam the lock mechanism.
2. Four barrel rivets hold the lock together and if these are drilled through from the swage side with a 4mm drill the oversize remains as sleeves and the lock side plates are separated.
3. The wear in the slot is caused by the very small area of contact between the roller and the slots, aggravated by the force of the springs.

4. The solution is to transfer this force to the face of the side plates and distribute it through washers held by a bolt.
5. A 1/4" Allen bolt was selected with sufficient shank length to avoid running the thread in the slot, the slots opened out and lengthened to suit this larger diameter and the socket head cut down to 1mm to minimize the extra width of the lock.
6. After lubrication and reassembly with the Allen bolt, thin washers and a nut, the lock can be riveted together. Cut down nails work well.
7. Having got the washers sliding smoothly, the excess of the bolt, used to hold with a Mole wrench during tightening, can be cut off and punch locked.
8. Unavoidably, the added thickness of the bolt and washers causes the new roller assembly to interfere with the lock mounting indents in the door. Spacers totalling 3mm are needed to provide the necessary operating clearance.
9. Equally unavoidably, the 3mm spacers will make it difficult to insert the pin which retains the door handle. It will probably be necessary to drill the square shank of the handle shaft at 90 degrees to the existing hole but 3mm further out.