Noisy E320 axle
 

I have a 94 E320 wagon that has had a nasty noise originating from the left rear on and off for the last 8 months. The noise is really bad when turning to the right and also is loud when climbing hills. I've had a hard time pinning down the problem till this morning when I jacked her up and removed the wheel. What I found was an axle that has a lot of slop in it. I can move it in and out by hand. I checked the other axle and it is rock solid so I'm pretty sure this is my problem.

Where's a good source for an axle?
Is it an easy job to remove and replace?
Are these known for being noisy once they go bad?

Thanks in advance!
Brad