back in the day of brushed r/c car motors, people used this water method to break in their motors (work in the motor brushes to match the curvature of the motor armature contacts)
if you want to clean your motor your better of using r/c nitro cleaner / motor cleaner to clean your motor. when you spray that stuff in a motor the stuff that comes out of it is nasty black crap.... not foggy white water.
http://www3.towerhobbies.com/cgi-bin...?&I=LXUSS8&P=7
other ways of improving motor performance of old well used motors include re-cutting the armature com, and swapping out the motor brushes.
which is typical in the world of brushed r/c cars, but not so much for air-soft.
the performance gains are easily noticeable in cars, i don't think its that big of a deal in air soft, unless your motor is realy realy worn out.