As I was changing the trnsmission filter on my 2000 f-150 5.4L I found a littel plastic pice that look like A spinning top. At the bottom of it there is a O-RING on it .

 

Its a dust plug used when the tranny was first built to seal the dipstick hole. When the truck was assmebled, they force the tube in and it pushed the dust plug into the pan.

Discard it.

This obviously was the first time the pan was dropped.

 

Thanks for the help CJK440.