See if the tanny fluid is going down when you ride.
If it's not, I would give pretty strong odds it is a jetting problem, not a leak.
If it is, I would give pretty strong odds it is a jetting problem, and the tranny is leaking from elsewhere. lol
thats my way of saying, I think it is probably jets, but it is possible that it is a tranny leak. Checking the tranny fluid will tell you if it is leaking, if it's not, you know where to go (jet your bike).
Assuming I am correct, and you find it to be jetting, do a search here and you'll find so many posts about jetting it will boggle your mind. You will probably even find some about jetting kx80's, maybe even a '96, who knows.... but give it a whilrl and then, if you have any questions after that, bring them in. (to the right forum)
Are KX80's considered 'mini's'? I always thought mini's was like the 50's and 70's.