Name this part

While replacing the gasket,filter and seals in my 904(1978 I think) I found this washer thing attached to the magnet in the pan.So does any body know what this is or where it came from.It's possible it's not a tranny part as I don't know much of the history of the car.So all you tranny experts chime in I ready to put the pan back on but I don't want put it back together until I know this isn't a major piece.It measures 1/2" x 1/16" thick.