The driver's seat in our 2005 Explorer cracked a couple of years ago and we ordered a new leather seat bottom from "The Seat Shop". It cost around $200 but it perfectly replaced the original seat bottom, fits and matches the original color exactly and you install it yourself. The directions were easy to follow and do. Your seat bottom is over 20 years old and I would suspect that it just reached the end of it's life, a long at that, especially in south Texas heat. Labor to "repair" a 20 year old leather seat might cost as much as a new good replacement and it's still 20 years old and who knows how long it'll last.
Whimsey