There's been quite a bit written about his subject, much of it rather dubious in my view, but the general story seems to be that the metal in the bearings was specified for Japanese oils which were higher in one ingredient than EU oils. As we learned in basic science at school, material will migrate from high concentration to low concentration to try to reach a balance. Now, it's interesting that some of the the worst bearings I have seen coincide with stories of people changing their oil more regulalry. If you think about it, the bearing metal is trying to equalise the oil (OK just go with that) and of course every time you change the oil and put fresh in, you start that all over again. We're not talking large quantities here. If you left the oil in for at least the 6k it's intended to do the leaching of the metal elements is less. I guess that the worse you treat the oil the better the bearings will be in terms of erosion. OK the lubrication might be poor, but the bearings will be great! The replacement bearings should all have the correct metal (magnesium v calcium or something) so that EU oils will be neutral. So, what you don't want to do is buy oil especially from Japan if you've just put ACLs in.