How to tell if alternator bearings are going......
 

Use a mechanics stethoscope.... check it when running.. put the probe as close to the bearing as possible .. it will sound rough....

Get the stator and the brush pack and call it good.

FWIW, alternators have slip rings, not commutators.

The bearings on a failing device will sound and feel rough if spun by hand. You can also grab the shaft and give it a wiggle and a tug. If you have ANY play, the bearings are toast.

There is no reason to ever replace the stator unless it has failed. It is nothing more than a coil of wire wrapped on an iron core. There is no "wear" occurring to it. It is either good or bad.

Check the condition of your slip rings when you have it apart, if they're grooved, replace the rotor. Resist the urge to sand the slip rings. If you feel like cleaning them, use Acetone and a clean rag. Nothing else. They should not have any sort of lubrication on them, the graphite in the carbon brushes in the voltage regulator is all the lubrication required.

You can also use a section of broom stick to listen for where sounds come from. The stick on the Alternator and the other end on your ear.

Watch out for moving parts.

I would worry that you are going to get made in China bearings (which cost about 2-3 dollars on ebay) from rock auto.

If you have the time you can take apart the alternator and the number of the bearing will be on them. Go on ebay and find a source that has USA or Japanese made bearings.

Note when I changed the Bearing on my alternator I found that the Alternator had a sticker saying rebuilt by Bosch North America. Chinese Bearings were inside.

It's easy enough to check for play without the belt. The rear bearing is easy to change, the front takes some doing. Make sure you don't damage the retainer plate, it's soft steel.

Well Rock was nice enough to supply the bearing number: NATIONAL 303CC Ball Bearing; Bore=0.6693", Outer Diameter=1.8504", Width=0.5512" Drive end

Apparely Rock Auto does calles it a communtator: Alternator/Commutator end bearing:

NATIONAL 201CC Ball Bearing; Bore=0.4724", Outer Diameter=1.2598", Width=0.3937" 70 amp

NATIONAL 201S Ball Bearing; Bore=0.4724", Outer Diameter=1.2598", Width=0.3937 55 amp

They can call it what they want, that doesn't make it right. Slip rings are just that, rings with a continuous contact surface that provide a slip connection (generally in pairs). A commutator is segmented (think of your starter motor). Old cars with a "generator" or "dynamo" had a DC generator and DID have a commutator. An "alternator" is actually an AC device that is rectified to DC through the diode pack in the rear end. AC machines produce an alternating current (hence the name alternator).

If they start rattling it's a tell tale sign you're going to replace the alternator in about a week when it exploded. It happened to me.

Don't bother replacing the stator. You're just throwing money away.

The brushes are part of the voltage regulator. Make sure you buy a genuine Bosch regulator. Keep the old one as a spare in the trunk. They're available all over the place, usually for under $40.

I just looked at a couple of youtube videos, and I don't like any of the recommendations for pulling the front bearing. They do things like snap the outer race in a vice and use dremel tools to grind the inner race. That's the hard way to do it, and if you slip, you've ruined the shaft. The right way to do it is with a gear puller. There's an illustration on post 10 of this thread (it's a different Bosch alternator, but the architecture of the front bearing is the same):

964 alternator rebuild - Pelican Parts Technical BBS

He removes it correctly. If done this way, the bearing comes out in one piece and the plate isn't mangled.