Antonio, let me see if I can summarize your challenge:

1. In forward direction, you have lights but no movement
2. In reverse direction, you have movement but no lights.
3. Before you cleaned the motor, everything (motor and lights) worked as expected.

With movement in only one direction, I would check the continuity of wires between the reversing unit and the field coil. That's an old locomotive, and one of the solder points may have separated while you were cleaning. In particular, the point where the wires connect to the field coil or brushes may be loose.

Good luck and let us know what you find.

Pat