Whilst applying brake after landing the pilot's foot slipped off the left rudder pedal and the aircraft veered to the right. The pilot replaced his foot on the pedal and applied corrective rudder and brake but the aircraft subsequently ground looped to the left and the right main gear leg collapsed. The rudder pedal surfaces were found to be worn. The pedal design was such that foot restraining capabilities were reduced as the surface became smoother from normal wear and tear. It was also determined that the brake pads on the right gear were excessively worn and this probably aggravated the pilot's problem with directional control.