I had this issue not too long ago. Bought two brand new OEM axle seals and the passenger started leaking after replacement. I realized I had pushed it in too far in the trans housing and it wasn't sealing on the axle. I don't think there is a stop for the seal on the passenger side. I bought a new seal and was careful about install depth and it seems to be fine. I think there is something that stops the seal on the driver's side, so not sure what the issue is there. This is all off the top of my head. I think there are other threads about this same issue.