I put it in drive and the car would drive a little ways then the engine would rev for no reason passing 3 rpm and then after a while I put it in drive and the engine would rev but not move at all it did this in every gear. Turned the car off for the night started it and it started driving but starting doing the same thing. The person I bought it from said it needed a transmission fluid drain
I think they meant fluid exchange when they really knew the transmission was failing . You can try new fluid but I think an independent shop will say you need a transmission.
Sounds like the transmission is already drained due to an unrepaired leak, have you checked the fluid level?
Perhaps a transmission service was recommended so that the leaking transmission pan would get resealed.