Sounds like you're getting to this problem just in time.

All the 240 axle half-shafts are interchangeable. I've actually done this repair both ways: replacing the bearings on the original shafts and swapping boneyard shafts for the originals. Swapping the boneyard shafts not only eliminates the need for getting your originals to a shop press, but also reduces downtime for your 240. Those new bearings are expensive, too.

However you go about it, you'll want to replace the inner axle seals with new seals. The outer axle bearings are lubricated separately from the differential: the bearings are fed grease while the differential lives in gear oil. The inner axle seals keep the gear oil and the grease separated. The outer axle seals keep the grease in and water and dirt out. When you're picking your boneyard shafts, pick shafts that show no sign that the outer bearing seals have been leaking gear oil. When the inner seals leak, gear oil from the differential gets all over the bearings, displacing the grease, and then seeps past the outer bearing seal. Those seals are placed on the shafts before the bearings are pressed on, so they can't be replaced without removing and re-installing the bearing. If they leak the bearing suffers and the leak can lead to trouble with your parking brake.

Make sure the wheel lugs are in good shape, too. I wouldn't bother with a shaft that shows sign of leaking at the outer seal, but if the outer seal looks OK and the lugs look OK, I'd pull it and have a look at the bearing itself. If the bearing is soaked with gear oil instead of axle grease then the inner seal has been leaking and you can assume the bearing has not gotten the lubrication it needs. Keep looking.

Once you find shafts without the above problems, look for discoloration or scoring on bearing and race. Excessive wear will be pretty obvious on the bearing outer race. Make sure to pull the bearing outer race from the axle housing and keep it with the shaft it belongs to. Used races should not be swapped around.

Before installing your "new" used shafts, be sure to pack 'em with new grease. Wipe as much of the old junk off without leaving too much lint behind, then force new grease into the bearing with a rubber-tipped grease gun. Just displace as much of the old junk with new grease as you can.

And your old shafts are not junk. They're good shafts with bad bearings. If you or a friend have more than one 240, or if you have a friend who may need to do this repair in the future, those old shafts may come in handy. You can reduce downtime entailed in this repair next time by pressing the new bearings onto your now retired shafts before you even take the next car apart. Then, when it's time for the repair you can swap the shafts and get the car back together in an hour or so.

One more thing: When you're pulling your axle shafts, you'll have to get your brake calipers out of the way. Don't bother to remove the hydraulic brake line. You can save the trouble of bleeding your brakes by leaving the hydraulic connection undisturbed and just making the metal brake lines loose where they are attached to the rear end. Make the lines loose then suspend the calipers up and out of the way by tying them to your coil springs with a lenth of wire.

Good luck with it!