a 4 magnet motor will fell like it has less magnet (spin freer then a 2 magnet motor)
KR and PT (which he has) are both 4 magnet
the only difference is
KR= MID COMM with laydown brush
PT= SMALL COMM with standup brush
so a PT is basically a TI with a 4 magnet can.
if the magnets feel weak it could be just an old motor the older they get the more the magnetic field gets weaker.
also if the previous owner left the motor in a metal box that can leave weak magnets.
so i would try it first then if you have a problem contact the previous owner.
John B- The HEAT issue is on both motors and batteries but its focused more on the motors. When the motor gets so hot it burns the brush because it burns all the lubricants once that happens it attacks the comm and as soon as the comm gets black or really hot the can is roasting and so it looks visually like the car is dumping the battery (which does hapen often) but it is actually the motor being so overworked it cant go no more. LOL