Price injectors and injector pump, dirty oil will cost more...
6000 hours on one M9 and 4000 on the other, always using drain oil mixed with the diesel fuel, never been an issue. In fact both have been in for an overhead adjustment and injector spray test, the 6K one last year the 4K one this spring. Both patterns are fine, pintles are fine, replaced nothing. Valves were out that far either. Steady diet of Rotella T6 5-40 with Archoil friction modifier additive in every oil change.
Your comment is baseless and obviously based on what you read somewhere, not actual practice.
I don't ever pre filter the drain oil either. Comes out of the oil pan into a clean catch container and into a clean 5 gallon plastic tote and from there, into the fuel tank and I let my Kubota spin on fuel filter catch anything of interest. I change my fuel filters, every oil change, never had issue one.
My powerstroke Diesel pickup gets the same deal. Been doing it since new in 97.
Diesels, in general will run fine on a lot of 'fuels' other than diesel actually.
Don't much care what anyone does, I do what works for me and I've been doing it for a long time with no adverse issues.