2000 MUSTANG TRANS LEAK helpppppp!!

I am in the process of purchasing a 2000 mustang convertible v6 with 103,000 miles. I went to the dealership took it for a spin everything seemed to work great shifted good,no wierd noises,brakes were good..etc. I drove the car to midas where they tested the car out for problems. They took it for a test drive first and said everything sounded good and it shifted great..they checked under the hood at all of the fluids and everything was perfect..now when the raised the car up the trand he noticed right away was leaking very little out of the output shaft seal. Then when he pushed up on the shaft there was a little bitof play he said. He told me that after driving it he did not think there was going to be this type of problem when he looked.

Qustions i have are: Is this a big deal? How long will the trasn hold up? Is this common with mustangs? Do i have anything to worry about? Should i buy this car if i can get it for 900 less?
Any information about this problem would be extemely helpful since tommorow is the day where i have to decide to buy it or not.....thank you for your help... :runaround:

my 1996 mustang GT V8 had a leak in the transmission and my mechanic sealed it but it was still leaking. Now my car will go backward but it will not go forward. What is wrong?