help choosing a motor

[RUSTED]

b4 ordering the flm hybrids i opened the rear diff to see wats the prob turns out its not the gear that stripped , its the case that somehow broke , the place the holds the spider gears and shaft in place in the gear carrier broke , so i went and i bought another gear case and the same problem happened again during the first run , should i get the aluminum gear carrier?? will it fix my problem? or is the flm hybrids the only way to fix the diff problem im having??