Selector shaft seal

The book shows replacing them as part of an overhaul, however they are both installed from the exterior of the case. As such it should be possible to replace them without tearing the transmission apart. I would suggest doing it as part of a service so you don't take a shower in transmission fluid. Drain the fluid and drop the pan.
https://www.2carpros.com/articles/how-to-service-an-automatic-transmission
Now to change the seal you unbolt the lever from the side. Then use some brake cleaner to clean off all the crud from around the seal. Then use a screw to pull the old seal out like these videos
https://www.youtube.com/watch?v=iQwulUnPxew
https://www.youtube.com/watch?v=Ehqz1Y-ggGo
Then use a piece of tubing or pipe to install the new seal.

The shaft goes through the transmission so it has a seal on both sides of the transmission. However if it's only leaking on the lever side you don't need to do both. They only list a full overhaul kit not the individual seals.

The better kit is available through the dealer, for the aftermarket kits you need the numbers off the transaxle so you get all the correct seals. There were a few minor changes made over the years. A dealer can give you the newest part number using your VIN number.

You're welcome.