Repair an angle grinder that stops working randomly - replace the carbon brushes HD

AMG workshop My old angle grinder started to fail from time to time, at first i thought it was a loose connection since it works after giving it a shake, but that strong burning smell and those unusual sparks confirm the problem was from worn carbon brushes, From my experience, the burning smell and those unusual sparks can also be caused by the friction of the non lubricated gears and bearings that prevents the rotor from rotating easily