Changing times.
In those days an engine had to be stripped down at least every 2000 miles for de-carbonizing, grinding in valves, filters washed, resetting tappets,etc.etc. Pretty well everything could be done with the toolkit that every biker carried and most riders were quite capable mechanics. I cannot remember ever going to a dealer for a repair or service - sometimes the blacksmith was required to do a bit of straightening out of foot rests etc. Now I find myself baffled by a plug change, but then they do last a bit longer these days. Of course a sparking plug could be taken apart and cleaned with a wire brush and the gap reset. Garages would clean your plugs by sand blasting, then test the spark under pressure - and invariably tell you that it was U/S - a plug costs 5/- which was a lot of money. Happy days!