lsd one? by the looks of the diff that one seems to be. Just look and see if the teeth on them are chewed up, the syncros are the gold thin sleeves before each race slides to lock each gear. its kinda hard to tell when they are bad just by looking at them. just see if you can see any abnormal wear on the 2nd gear cyncro compared to the others. the syncros also like to wear on the portion you cant see thus being hard to tell. haha.
congrats on the find, you can send one my way if you want, yeah its easy to open up the case it gets more difficult when you go to take the shift linkages and forks out and then the gearset, then the hardest is getting it all to slide back in there all inline. the forks are a pain sometimes especially on those b15 ones the setup is almost identical to my old mazdaspeed protege tranny that i had to rebuild. the shift linkage has this little ball and spring you have to keep pushed into place while you slide the whole gearstack and shift assembly back in. pain in the butt.
it helps to have someone helping you holding the bottom pieces while you slide it back in.