That is a Super Motor. Kinda pain to work on, but lubrication is a must and the brushes must be contoured to the commutator, if replaced. The brush holders have a clip that will retain the brush springs when replacing the brushes. The brushplate is removable, but to do that the original brushes have a hole drilled through them to retain them when reinstalling the brushplate. I usually just leave it in place, pull the springs back and use needle nose to replace the brushes. There is a phenolic ring that retains the segments of the commutator. If cracked, the segments will fly apart, damaging the windings.
This may help; original Lionel instructions.