I’m on my second 6,5l diesel in more then twenty years. I have replaced the starter on both motors due to intermittant cranking failure. Shall try to explain why.
Suddenly, after years of reliable function, the starter refuse to crank the engine, I can hear a ”click” from the starter. I turn the key to START couple of times and starter will crank the engine. Now it works OK for weeks but it will happen again. Over the time it will happen more And more often until It get unpleasent, like shall it start or.....
I will replace the starter and now it works for years and then it start the same all over again.

What can it be for reason ?
Somebody with same experiance ?