Do you kow the current condition of the transmission? Is it working OK now?

While I'm no transmission expert, I have gone through several automatics and had fine results. If the transmission has no known problems now, I think it's an excellent opportunity for you to get into it and give it a freshening up. Buy a complete rebuild kit, and be prepared to pay real close attention to every part that you remove, looking for wear, damage, etc. If you replace all of the wearables, seals, gaskets, o-rings, clutch plates, discs, etc, it should go pretty well. Make sure you're prepared to have little parts laying out in clean surroundings, have lot's of little plastic bags and a magic marker to make notes.

What I myself wouldn't consider doing, is trying to diagnose a problem(s) on a transmission that's not working properly, say one that won't shift, or that has bad slippage. I'd hate to spend all of the time to "rebuild" it, and reinstall it, just to find out I mis-diagnosed the problem, or didn't completely correct the initial cause of the problem!

Good luck, and have patience ( and a quiet place to work)!
Russ