I think those slots you're refering to are there to hold the magnets in place at the bottom of the can (there's a spring clip at the top) If you want cooling then you would need to cut more holes similar to Slotit and some of the Sun motor configurations. The best thing you can do to keep motors cool is reduce friction. This can cost anywhere from nothing(align everything properly) to a few Euros (adding ball bearings and balancing the armature).
Also you're better off using isopropyl alcohol to clean comms in the motor. Chance of fire is greatly reduced.
Jimmy
Also you're better off using isopropyl alcohol to clean comms in the motor. Chance of fire is greatly reduced.
Jimmy