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Thanks for posting
The only place it can leak ATF there is the front oil pump seal for the transmission, the oil pump has a seal for the torque converter and an O-ring that goes around the outside of the pump housing, once the transmission is removed the entire oil pump can be removed and the seal and o-ring replaced, a special tool/puller is needed to pull the pump out, the torque converter output shaft should be checked for any grooves or wear that can cause the seal to leak and if necessary the torqe converter replaced if there is any execessive wear. In most cases it is only necessary to replace the pump seal.
What I would recommend is to try to find a reconditioned transmission, it sounds like this one is getting very tired and those shifting issues are probably due to worn parts and clutches wich causes internal pressure loss, maybe even a used one but then you never know what you end up with. I had a 4 runner about 15 years ago that was kind of doing the same thing plus it wouldn't go into overdrive until it was driven for about 5 miles or more I was going to take it apart and rebuilt it which I used to do many years ago but could not find any commercially available kits so I got rid of it, they wanted $1800 for a "reconditioned" one from a junkyard and it was probably only worth about $3000
The torque converter seal can not be replaced without removing the transmission.