Diff side output bearing question

After replacing all the bushings, struts and springs and putting in a Ron Tyler Diff mount, I finally found out where the famous rear clunk problem is on my 1978 280Z. It is clunking where the axle flanges go into the side of the differential. I can push, pull and rotate the flange and feel the slop while I'm staring at it. My question is; is it usually the side output bearing that goes bad or or the gear teeth on the companion flange to the diff gear itself? Can I replace this bearing with the diff in the car? Most of these rear clunk problems seem to come from other areas such as the diff mount or the U-Joints. Mine are good. Thanks for any info!

Dan Frye