Replace the condenser. If that doesn't work, replace the rotor arm. Neither is expensive, both will give you useful spares to carry in the tool box. If neither works, look very carefully at the strap which goes round the outside of the points plate from the connection on the side of the distributor to the points pivot. The connection stud should be soldered into the strap. If it has become unsoldered, the resulting problems are a swine to trace. If you have a lot of play between the cam and the distributor shaft the easiest solution is electronic ignition.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), 54 4G Mk IV (project), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser.