northern grits

2000 4x4 5.4L only 47,000 miles. Discovered a dinner plate size drip in driveway after a few days of the truck sitting. Noticed the rubber cap is missing and some (transmission?) fluid on exterior of the pan and whatever the housing is the cap is on (please see pic).
Do I need to replace the cap? What happens if I don't?

jkenprice1

If you have tranny fluid coming out of that hole, your front transmission seal is probably leaking. replacing the plug won't stop the leak.