hi phil mate
yes if your missing a brush you motor is done for. put it on a shelf to remember your self of the first motor you killed.
you can replace the brush but that depends on the end cap ( where wires connect) if this is inside the motor can and has small tabs holding it inplace you cant replace them my mini t moter has no replacable brushes too so will soon be in same boat mate
i would sugest getting a graupner 300 and better esc when money is more available these motor are very good and dont cost a fortune, you may require my good friend dremel on the mount but a little bump an grind for more speed and fun is well worth it
TC