Usually the brushes are worn out. If you took all the screws out of the plastic end cap where the wires connected and it still won't come off, Try some gentle persuasion. Was there a spring clip retaining the electrical connector to the end cap? Sounds like there was a screw holding it in place.

You may have a Siemens motor, a little unusual. If the motor housing looks like a solid can and you can't see the motor's commutator, that's probably the case.

The more standard motor is the Bosch version, which is pretty easy to overhaul. The brushes are easily accessible on that model. On the Siemens they're hidden under the squirrel cage.

If you have a vise and a drift you can drive the armature shaft out of the squirrel cage. But first, get the end cap off the other end of the motor to see what you're dealing with.