stopped and started

On Saturday I got about 100yds in the car to Truro when it went duuuuurh! I gave it a few attempts on the starter then with my wife driving and my daughter helping, pushed it back home. We went into town in another car and at the park and ride there was a yellow X19 belonging to a friend. a red and yellow parked would have looked good. I bought a new fuel filter as it needed one anyway and that afternoon started the inquiry. I cleaned the jets, fitted the filter and tried again. A faint catch but then nothing. I had a good idea and took the battery out to charge. It was getting cold so I slept on it. Next day I looked at the filter in the carb but it was clean.
Oh dear, it must be the spark and my wife who holds the spark plug at such times was at church. I got to grips with the distributor access panel which I hate doing and had a look. The cap wasn't fitting properly, it was loose. I cleaned and tightened all the connections and fitted a new rotor arm which I had and it started immediately. Have any of you noticed a cap become loose, unseated?

I really don't like the clip-on caps. Much prefer the screw-on type. Feel much more reliable. The clip-on type are so easily moved.
Good detective work though... always satisfying when ya fix it for nowt