It lives! It appears to be the ignition switch, as these are known for getting grungy after years of use, and are affected by extremes of temperature. Well, it was extremely cold when he was trying, and failing, to start the beast, and once the weather took a turn for the mild a few days ago the thing cranked and ran like a Swiss watch.
Spring project will be to remove the ignition switch, clean the contacts, spray with some of that magical electrical stuff, reassemble and keep fingers crossed, which is supposed to work. Except the crossing of the fingers, the jury is still out as to its effectiveness.
I shall have to be the primary technician, as my brother's philosophy of auto repair is to pull out his chequebook, which with a Porsche will rapidly lose its appeal. Who knows, maybe I can make a converted gearhead out of him?