JW411:-
I find it quite mind-boggling that they even tried to use re-cycled oil.
Quite agree. Ancient as I am even 1950 was before my RAF career, and the Hastings 1's were powered by Hercules 106 engines (1675 bhp) then, for what that's worth. I can't tell you what I've just come upstairs for, but the words coring, sludging, and Solomon Dampers will remain with me to the very end.
Our Flight Engineers (for whom we give thanks to the good Lord) were very much on top of such nasties as you describe and I do not remember any incident of either malady, so Mr Solomon's dampers went on turning, doing whatever it is that they did (damping?).
As far as I know all our POL's were fresh out of the tin, and such nasty dollar saving practices as recycling them for reuse were things very much of the past.