Yes, open the motor up. The method of squirting grease in is for sealed bearings, which are ball bearings. The bearing in the motor you have is a bronze bushing that the shaft rides in. Opening the motor should not be a big deal. Just be careful with the brushes, the are carbon and brittle. Don't get grease on the brushes or the surface they ride on. What do you have to loose, if it does not work you will buy a motor which is what you would have to do if you don't fix this one anyway.