You can now purchase the hardened splines to repair your TF81 differential.
The TF81 (aka AF21) valve body has undergone some changes that you should be aware of.
Have you ever installed a TF80, TF81 or TF60 after overhaul and it has had harsh shifts or engagements, or maybe there has been a flare/bump upshift or harsh coast-down clunks? Most times, clearing the shift adapts and driving the vehicle to relearn the shifts will correct these annoying problems. After a good, long test drive to relearn the shift adapts, sometimes a shifting or engagement problem remains. Assuming that there is not excessive wear in the valve body and the linear solenoids are good, the clutch-control valves on the valve body can be adjusted to correct these problems.