You need to look upstream of this position and find out why they are "oxidized." Were they rinsed in something? What was the machine cutting fluid? You need to understand the chemical reaction that produced the "oxidizing," It may not be an oxide at all, but another compound formed out of an adverse reaction with something in the process up to this point.
Until you understand what you have, you cannot form a competent method of correction if it is at all possible. The "oxidizing" needs to be looked at by a Metallurgist to determine if there is pitting, how deep and what ramifications are there as a result.
Just looking at the parts and asking on a forum will do no practical good for what looks like some expensively machined or die-cast parts. You need professional technical help here!
At a guess and not knowing the cause, I would suggest scrapping the lot and starting again. Especially so if these parts are for a customer you would like to keep for future orders. Think of the big picture.