Electrical motors can have a "burn off" period, but it's not really suppose to be like that. I think the explanation is dust and grime gathering over the decades around the copper parts generating the electricity. Motors aren't sealed off, they need the ventilation. Another thing is wrong lubricant, if oil seeps along the motor axle; it's suppose to stay at each end of it. You can take a chance on having a single (!) drop of oil down the grease ports; the wicks are often clogged up by dried up gease, and it will not overflow the motor. The correct thing to do is of course open the motor, clean and regrease and it will be mooth and non-smelly.
New carbon brushes can be a bit noisy, apparently even make sparkles until they are run in. If you can make a curve at the end of them exactly the same as on the motor part, it will prevent an run-in roughness.