I agree with you Jim, things that fix themselves when you dismantle and reassemble them have a problem that will probably come back. In this case it is very likely to be a bad ground connection or chafed-through insulation on a wire somewhere. How does the coil's ground look? It is fairly common to have a problem with that because the coil is mostly made from steel and it forms a voltaic cell where it clamps to the aluminium engine. The aluminium oxidises and forms an electrical insulator. Cleaning both the aluminium and steel parts then reassembling them, fixes that particular fault for years.
