1) You're a moron for even taking the chance on paying $4000 for this. It was pretty reckless to not get a written guarentee on a goodwill from Honda. That's a ridiculous price. I got mine fixed for $950 installed, and the V6 tranny costs more and is harder to replace.
2) You should have looked into whether it was the original tranny...I've never heard of fluid leaking from the seals unelss the seals had been replaced. My seals leaked when I had the tranny replaced...had to replace the seals 3 times.
3) You might want to consider taking legal action against the previous owner if you actually have to pay $4000, as he probably knew that the transmission leaked fluid and/or had it replaced.
4) It is extremely rare for a Honda auto to go before 100k unless it's been abused. 4 banger trannies typically last 200k. Something is seriously wrong with your situation and you should have done more research into it before giving it to the dealership so they can rape you.