1990 Ford Escort Transmission Fluid Leak!

Well I am not the first owner of this car so when I got it there were a few problems. I put a rebuilt engine in it after it sitting for a while and had some break work done but otherwise its been driving perfectly. Around August of this year I noticed that while driving the gears werent shifting properly or would shift when I was at a complete stop. Eventually it came to the point where the car wouldnt shift at all so I took it and had a rebulit transmission put in it. That was a little over two months ago that I had this done. So today I notice that again the car wasnt shifting properly and figured that it had something to do with the fluid and it did. I was told that there wasnt any in there so I went and bought some fluid and had it put in only to see in on the ground when I pulled off. So my transmission fluid is leaking but I dont understand why if I just had the thing replaced. Ive put a pretty penny in this car over the last couple of years so I really dont want to waste anymore money on it. So what are potential problems and cost that I could be looking forward to and is it worth fixing even though the car drives fine despite this problem?