When you get the oil pump off, pull it apart and clean it, when its back together, turn the pump gear, and see how tight it is, if the car it was previously in was smashed, it may have caused the pump to hit something and bend, it is very common for this to happen with subaru's, haven't seen it happen with a 4a, but would be good to check, might save you doin the job again, might save your motor one day.
Cheers
Rhys
