2000 S-class rear axle center section out, where to go from here?

[atikovi]

My 70,000 mile car has a loud rear axle whine when you are coasting and most noticeable between 10 and 40 mph. When you get back on the gas it goes away. I disconnected the axle shafts and tried it again with car stationary and it still made noise when going to 2000 rpm and lifting off the gas so I know it’s in the center section. I took the unit out thinking I’ll just get a used one from a junk yard but now that I think about it, isn’t there something I could try and fix first for less money than buying a used piece. A few things I noticed are that the pinion has some play in and out as well as side to side as if the bearing is loose. Also, you can turn the pinion clockwise and counterclockwise when you pull it out, but if you press in on it, it only turns counterclockwise. Any suggestions were to start. I have the WIS service DVD’s but there is no info on internal repairs. Does it mean these are not repairable?