Since the transaxle is sealed and major involvement in repair, I thinking about drilling a small hole om the case and putting some transmission fluid in the hole to fill the lost fluid. If it works I can use JBweld or fiberglass plug to seal the hole if it's not pressure bound.
As it is, the mower is useless to me.
What do you all think about drilling a hole?
Very bad idea.
Hydros are assembled in dust free environments for a good reason.
You may as well smack the tranny with a big hammer.
As already advised, you drop the tranny, remove the plug tip it upside down to drain the old oil then refill with fresh new oil.
The problem we have giving you advice is you have the mower in front of you and we have a screen.
Backe 24 years ago that mower could have been made by AYP, Murray, MTD, Rally , Noma, Bolens, etc etc etc etc
And they could have used any one of a 1/2 dozen different trannies.
The tranny makers that are still standing have repair &/or service manuals on line & the Tecumseh / Peerless ones are also on line.
But without the Craftsman numbers we have no way of knowing what is in there.
Modern trannies have stickers on them in 3 places so techs can ID them but back that far we would have to look up part listings, which many here will happily do for you, if you just tell us what the craftsman numbers are from the tag under the seat.
Nothing else really matters as the same model decals were put on a variety of different mowers.
Failing that as many photos of the tranny as you can manage.