I don't think it's the needle bearing. Air never flows through
the main body of the airbrush, the only thing that should be there is
paint. The needle bearing simply keeps paint in the front of the
brush. Air flows through an air passage, through the head, and
AROUND the nozzle. This creates a low pressure area that pulls
paint through the nozzle.
The most likely culprit is dried paint in the air passages and / or air
valve. Unscrew the head assembly and you'll see a hold bored
along the bottom of the airbrush body to the area where the air valve
screws in. That's the air passage and occasiionally paint will
accumulate in there. You can use pipe cleaners soaked with
lacquer thinner or tiny inter-dental brushes to clean it out.
Also check the holes on the head assembly. There should be about
six of them and you may need to unscrew the crown to see them.
To disassemble the air valve, remove it from the body. Look on
the bottom where the air hose screws in and you'll see a hexagonal
hole. Find an Allen wrench that fits that hole, and carefully
unscrew the end of the air valve. There are a spring and plunger
inside. Hold it over a box top or something so that if you drop
things you can catch them. Clean the air valve body, spring, and
cap with lacquer thinner. The plunger has a captive o-ring on
it. DO NOT use lacquer thinner on that as it could admage the
o-ring. Just use alcohol on a q-tip.