When removing the mag roller sealing blade, the magnet end foams and the mag roller sealing blade end foams will become damaged and should be replaced. HP 4200/4300 toner hoppers require a mag roller magnet end foam to help prevent toner leakage. During the cartridge cycle, the cells of this foam become compressed, and toner builds up on the surface. Foams that are pitted, torn or damaged should be replaced. Static Control offers quality mag roller magnet end foam replacements.