There are few things I am certain of, one of them is that taking an engine that has been running on monograde non OMD oil, and then starting them on OMD mid life is a bad thing.
Why,
OMD oils, were initally designed for diesel engines, was designed to remove carbon from the engine and increasing engine life.
The cyclinder bore on non OMD engines has a certain level of carbon on the mating faces as a normal thing, when you ad OMD, the carbon is removed very quickly and where the carbon previously formed a part of the close tolerance, air and oil can flow less restricted.
So, IMHO if you change an engine, any engine, petrol or diesel, to OMD mid life you will quite probabaly reduce the life of the engine.
As for carbon destroying bearings, no offence, I'm not convinced.