When attys are new I break them down completely. All screws out, all o-rings off and I put the parts into a container with snap on lid. Half fill the container with very hot water and a little Dawn dish soap, put the lid back on and shake. Then I empty and rinse under cold water to get all the soapy water out. Drain the container again and shake Baking Soda liberally on the parts almost covering them. Pour half the container full of white vinegar and lit sit until the effervescence stops, shaking occasionally till it is completely done. Rinse everything in a strainer under cold water and set out to dry on paper towels.
I have done this with every new atty that has arrived here and have never had that good ole Fasttech taste on any of them. You have to remove all screws and o-rings, as machine oil (The Fasttech Taste) will get in the screw holes and under the rings.
When I am drying the parts for reassembly I thoroughly inspect all the parts for swarf, burrs and left over bits to be cleaned out or passed under the Dremel a few times.
Twist up paper towel and put it through every air hole as best as you can, you would be amazed at the little bits of metal that can sometimes be pulled out.