They last longer than you would imagine but a tefc is the way to go
long term. Resist using compressed air when you clean, vaccum instead
or split the bell and clean with a vacuum and brush.
You would be amazed at how much crap you can keep out with just a piece
of light flashing bent to be between the swarf and the motor.
If you have to buy a motor buy a tefc, other wise use what you scrounge.