Question on permanent magnets in electrical motors

[A383Wing]

everyone knows there are permanent magnets inside the wiper motors, window motors, starter motors..

here's my question: Do those loose their "magnetism" over the years? Could this be why the motors don't work very well anymore with a load on them?

[bakerhillpins]

I'm no expert on magnetism but a quick google search turns up this old article which basically states that in general no they don't unless they are are subject to some sort of demagnetizing forces. Which apparently includes striking them (see second link).
http://www.gasenginemagazine.com/gas-engines/recharging-magneto-magnets.aspx

I found this link interesting too as it describes the basics with iron magnets: (the 2nd answer)
http://physics.stackexchange.com/questions/37989/will-two-magnets-lose-magnetism-if-they-stick-to-each-other-for-infinitely-long

An excerpt from this link.

Once you've magnetised your chunk of iron it will stay magnetised without needing any extra energy to maintain it. To demagnetise it to need to randomise the domains again, and there are generally two ways to do this. Firstly you can heat the iron until the thermal vibration of the atoms overcomes their tendancy to line up. This is called the Curie temperature, and above this temperature the net magnetism disappears. The other way is to take your piece of iron and start remagnetising it in the opposite direction. If you stop halfway you end up with no net magnetism. This is essentially what degaussing does.

The point of all this is that if you line up two magnets so their fields align with each other the magnets will stay magnetised, and can even increase in strength if you wait long enough (though you'd be waiting a long time). The converse it that if you line up two magnets so their fields oppose, e.g. north pole to north pole, and wait long enough their net magnetisation will decrease.

In both cases the change in net magnetism is due to thermal fluctuations within the iron, which is slow at room temperature. You can speed up the process by hammering the magnets.

I suspect that the biggest problem with these old motors is that they need rebuilt - they are sluggish because they are expending most of their power to overcome binding/friction. Bushings/bearings and the brushes would probably be where I would start. Also look at the transmission that is used to move the window as it's probably loose and generating losses.  Note that the first link suggests all the mechanical/electrical fixes before any "recharge" operations regardless.