does anyone know the difference between coreless and brushless servos

think it's two different things. a coreless motor can be brushed or brushless. Coreless has to do with how the motor is wound. Brushless motors use electricity instead of mechanical means to turn the comm. Not an expert, search wikipedia for "electric motor" for better explanation

From Futaba's site -

"Coreless motor
In a conventional servo, the motor has a steel core armature wrapped in wire that spins inside the magnets. In a coreless design, the armature uses a thin wire mesh that forms a cup that spins around the outside of the magnet eliminating the heavy steel core. A coreless motor does not have magnets as standard servo motors do, so they have a smoother, more constant, and stronger action. Regular servo motors have either 3 or 5 magnets (poles) which when the armature is between these, the servo motor is at its weakest."


Brushless -

http://www.futaba-rc.com/servos/brushless.html