I would caution against spraying anything into an alternator. As csf03716 says spin the alt by hand and if it feels rough it's time for bearings. Any decent shop manual should give you pretty instructions for doing it.

The good news is if you can do it yourself bearings and brushes (if it needs them) should be around $15. Bad news is if you send it to a shop to do your looking at about an hours labor ($50-60) plus parts mark up.

Before you do anything I would recommend electrically checking the alt to help decide if it's worth rebuilding. First check the voltage by running the engine at about 2000 rpm with the headlights on. If you don't have about 13.5 volts the alt is not putting out enough. If the voltage is low check the regulator if it's an internal regulator, there is a small hyole in the back of the case (again the shop manual will show you where it is EARLY GM ALT ONLY ) Insert a straightened paper clip or similar object in the hole. This in effect by-passes the regulator and full fields the alt. If the voltage comes up, the alt also needs a regulator. If the voltage is still low, you have either bad field or armature windings or a bad diode set.