OK, thanks Bill. I'll look for it in that spot. In the meantime, I pulled the cover off the differential. I don't see any damage and didn't find any shavings in the bottom of the pumpkin. All looks good. Someone has been in there, though, judging from the blue Permatex.
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When I re-install the spacer, the manual calls for .014 clearance between the gears and the spacer on each side. I'm going to try for this but there doesn't seem to be any way to adjust if you're off. Or is there? I'm also going to try and post pics of the axle removal as I go. I figure it might help the next guy who's doing this for the first time.