Transmission Question?

ok so i was lookin at some other answers and found a good answer to my first question. i got a transmission, the kid said it worked, when i put it in, it didnt. so in another ? i found use lubeguard for valves that are stuck, which i did. now it shifts no problem.. (well that day at least so hey musta been stuck valves) now the cars been sittin for a day and i started it up, now it wont shift n more.. whats wrong? if i have to buy that fluid every day that i want to drive the car thats crazy.