As I recall the circuit, doesn't fluid leave the converter then go to the cooler? Anything of mass within the converter will perpetually stay there. Sort of like throwing water from an old tire. Some Ford converters, including AOD and E4OD have drain plugs. Great idea for purging crud from the system. I wouldn't consider changing fluid without dropping the pan. What's laying there is telling of problems. Regarding fluid, it's a matter of whose friction material is being used. If current generation Raybestos or Borg Warner, use current spec fluid. If aftermarket, then designer fluids are OK.
