2 1/2 years ago I replaced a dead tranny with a used tranny I got from the yard. It ran just fine for about 6 months then one day I put it in gear and it did not move for about 60 seconds the bumped, went into gear and I did not have more trouble with it that day. The next day it did the same thing so I put a pint of Lucas in it and it never gave me any more problems for the next 2 years until tonight. I'd driven the car and parked it, then went out to put it in the garage several hours later and it happened again. I put it in gear, rev the engine and it does not move....then after about a minute it kicks hard into gear and then seems to work fine. I did notice the fluid appeared a bit brownish. Ideas? Tranny about to die again....and recommends?