How complex and critical things have become ! Admittedly, I was a late starter, only getting into motorcycles in 1970, aged 17, but the information then, passed on by the old timers, held true ! I got my first Triumph in 1976 ( bought new, and still in my possession !), and the then available knowledge , still held true !
I can remember quite a few Triumphs being rebuilt with the then available genuine parts, and which went on for reasonable mileages ! And , believe me, many of these rebuilds weren't "tool room " jobs !
Now, it seems that parts available today ( of which I have some that surpass anything available in the day ) must be the reason why Triumphs, for instance, must be rebuilt to standards of far higher than that of the original factory builds! To compensate for builder ineptitude ?
I'm not meaning to be disparaging of the gifted few who can build to the standards of factory racers, but the production bikes never were, and ( mostly) functioned satisfactorily .
Cleanliness and factory torque and adherance to clearances are the keys to successful rebuilds !
That's my take, so, in the words of Harry " the Breaker " Morant, to his firing squad, " Blast away, you bastards !"