Replace the set, If you put it back together with no new gear or just the replace the bad gear who's to say another old gear will not fail next run ? Diffs are to much of a pain in the ass to take chances.
2cents. BTW, Great Pics.
I retired from RC, now life is all about guns and long range shooting.
Hold the cup and one outdrive in one hand (don't allow it to move), and try to rotate the other outdrive back and forth with other hand. If it moves back and forth more than a tiny bit, it needs the shims.