Hi Greg - For all of my needle type AB's, I sometimes find slight paint residue on the needle mid section, not always, but it does happen. I use the Regdab lube, that seems to minimize it, I've never had residue travel past the rear end of the needle bearing, into the body. Once the needle is removed, (as you said always to the front,) I use a bulb type pipette and the appropriate thinning agent to flush fluid through the needle bearing, at least two or three times.
IMPORTANT, always hold the AB facing downward when flushing through the bearing, or residue can enter the trigger valve assembly. Don Wheeler has an excellent example of a dental mini brush tool he made, posted on his site. I have one now, (thanks Don,) used with thinner it does a super job of cleaning the more difficult areas, it easily passes through the needle bearing as well, (if needed).
Tip wiping at frequent steps as you spray seems critical, buildup causes problems in more ways than one. Small cotton pads with a drop of thinner swipes them straight away, just a habit for me now, works great. I don't spray thick materials ever, even primers are reduced considerably, just takes more passes but results in better finishes and less details lost.
The bearing is actually pretty durable, just don't force any thing through it that may have sharp metal ends, that could mar the internal surface. The very long toothpicks that can be found work well, they can sort of scrub the sides as you gently move them in and out while wet with thinner inside. Again. always facing front side down. (Took me a while to always remember this.)
Patrick