It makes sense replacing them if they leak and the forward one goes to the tank drain the rear is to the the non return valve. The one Ruzzle was reffering to is the tank drain plug that goes into the bottom front left of the oil sump pan You pull it everytime you change the oil. And actually the non return valve has a O-ring on it also. I will take some pictures later tonight and peice together a discriptive view to clearify. The ones up top that you changed have nothing to do with the oil leak down to the sump just they just stop the tank from leaking on the top of the tranny right under the tank and drifting to the back of the engine freaking people out because they think they have blown a head gasket.