I can't offer much help, unfortunately, because I've never worked on a
syncro. Have you compared the bearings on either side to make sure they are
the same number, size etc. Wrong parts do happen. With the hub off the
spindle do the bearings turn freely in their races by hand? Maybe you could
clean the grease off and look for foreign matter, contamination or other
damage.

Also, a word of caution. I once screwed up a wheel bearing job on an old
beater Nissan which I eventually sold to a friend I work with (read: big
mistake). His right front wheel locked up on him at about 40mph. (Man, did
I take a lot of crap at work from all the car guys.) I split the repair
cost with him I felt so bad. I, at least partially, blame it on the cheap
Chinese bearings I bought. My point is bad things can happen with wheel
bearings so proceed with caution. I was lucky.

Tom Brobst