filter? not all of the auto boxes have filters, in particular most of the facelifts do not have filters, but we haven't been able to determine a date when mitsi changed this. You may want to check that first before you order one!
It sounds as if your torque converter seal has started leaking quite badly. What you want to do is to get some SPIII or Amsoil ATF and fill it up to the correct point, and disconnect the battery terminal for 10 minutes or so.
Then go for a drive and see what happens.