why wont axles go into read diff??

I've changed out front axles a few time but haven't had to change rears. I just swapped a wrx drivetrain in my RS and got the front in but the rears seem to go in 50%. Its like the teeth don't match up in the rear.
the rear diff is from an 02-03 (not sure) auto wrx that was wrecked and parted out. The axles are the duralast gold from AutoZone (for 02 wrx) Any idea on wtf it happening? I tried what I thought were the old axles in it and does the same thing. I believe the diff is bad from the crash but not fully convinced