the fact that people must learn to accept is that these motors were never designed to be used in a force feedback environment - in other words to be put in a constant state of stall.
i too have gone through the trouble of having to locate and replace a burned out motor.
in my tests i have peformed i have seen these motors run way above the temperature limits that they were designed to accept.
to put it simply the rs-555ph series motors were for use in inkjet printers which would require that the motor be able to spin in both directions at a fairly high r.p.m. and a very small load.
now take this same motor and use it in a wheel and force it to run under almost a constant stall rate - the result would be much higher temps than acceptable and eventually the carbon brushes will weld them selves to the armature posts.
when we set the force feedback setting high and hold the wheel from turning we are forcing the motor to be in a state of stall - something that the motor is not designed to do.
so if we expect to keep these motors running well we need to reduce the ffb settings in order for them to survive.
here is a link to the motors intended use.
http://www.mabuchi-motor.co.jp/en_US/news/n2000_0410.html