Tamiya trf501x we center pulley problems

[chokoboy]

Im having problems with my 501x we 18t center pulleys(53989), i have replaced the center pulley 3 times the last 1 and a half month. The inner pulley that goes on the rear belt is melting, could it be that my slipper is set to tight? or that my rear belt is to tight?
Does anyone have any experience with the alu 18t center one-way (54051)?
It looks much stronger then the original plastic pulleys!