The bearing location you speak of (on all power tools) is usually a non-serviceable sealed/enclosed type bearing or a sintered bushing. In either case the only oil that will actually make it's way into the bearing is a light household oil. If I want something heavier I will first treat with a few drops of a light oil (wd40, gun oil, 3-in-one, etc.) then chase it with a drop of 20 weight motor oil. The idea is that the light oil will allow the heavier oil to draw into the bearing.
If there is a bushing and you can extract it, then just take it out and let it soak in wd40 (or similar) for about 5 mins. Let it drip dry or dab it dry with a clean rag (no wiping), then re-install and your good to go.
Again, these bearings are usually not meant to be serviced. Take caution not to use too much oil...only a few drops. You don't want oil making its way onto the comm or the brushes.
