We have found an alternate way to free up sticky rollers on Mecanum wheels. It appears that sometimes the urethane gets into the bushings at each end of the rollers. It is also possible for the diameter of the hole in the urethane between the two bushings to be smaller then the diameter of the hole in the bushings.
http://www.youtube.com/watch?v=1mrNH0Czq0I
Thanks.
Phil