1994 Other BMW Models Tranny fluid leak- can I top it off?

Mechanic says the tranny has a leak. I'm trying to sell the car so I don't want to put $$ in to it. I don't notice any mechanical difference (no trouble getting into or out of drive, reverse etc) Car shifts fine. I do hear a whinning sound for about 3 blocks as the car warms up and you can hear it change pitch with the shifting. It goes away in a couple of blocks and does not return until the next morning. I wonder if I just topp off the fluild it will be fine until a new owner wants to tackle the real issue. Over the course of 3 months, I also had 3 times the car stall after I put into drive. It may have been I did not wait for car to warm up, or maybe its something else. 1) can I add tranny fluid myself? 2) is the fill hole accessible. Its not in engine compartment 3) do the STOP LEAK type products work? 4) do I have to buy the tranny fluid from those overpriced dealers? Many thx