For brushes I use the Trinity #4505's. (cross cut high silver) The #4499's are also fine. With most of the motors the purple (pos.) and red (neg.) or the red (pos.) and green (neg.) springcombination works perfectly.
Furthermore cut your comm, put new brushes on and make sure they are seated well! (run the motor for 300 secs at 2 or 3V)
You can also use comm drops. I personally always use Zubak's SpeedJuice. (www.speedjuice.com
) Tribotech Powermatrix also seems to be a good choice.
Last but not least; gear your motor the right way. Make sure it doesn't get too hot.