Hot bearings to me would say they have a bit too much friction going on, so, best replace them, they should warm up not not get very hot (though the scale of heat you don't mention, too hot to touch? Burns your skin? feels like hot water from a tap?)...
Grease is fine, infact it's what you're meant to use in ball bearings, but you should clean out the bearing before repacking really, but since you're replacing anyway I don't really need to describe the process in detail (involves soaking the bearing in a solvent, rotating it so it clears out the old grease and metal fragments, then drying it off and repacking), though repacking an old worn bearing is pointless, the easiest way to tell how good a bearing is by moving the armature up & down, if you have movement, you have a bad bearing which will howl and grind no matter what you do... :S
The rear bearing is a bit tricky to remove, you need a bearing puller tool to remove it, but putting it back on is easy enough (just tap it on, don't hit the outer ring though cos you'll destroy it before you even get to use it!!)...
And the electric contacts, assuming you're talking about the motor brushes, are known as Carbon brushes, being made of carbon of course, if the ones you have are really short (quarter of an inch or so), then yeah they need replacing, but if they're longer (Half an inch or more) then you don't need to replace them yet...
