I have a 2004 Ford Ranger with a 4.0L V6, 86,000 miles. I just did my oil change and noticed a small leak near the transmission pan. I noticed it was leaking from this square bolt. I tried tightening it but it wouldn’t budge. It’s not leaking a lot. I’m guessing it’s been leaking for a long time but it’s very slow. Trans fluid level is perfect still. Should I just leave it and add trans fluid if ever need to? Heres a photo of the bolt: 
it could be a pressure testing port. Some pipe sealant might fix the leak. But as you say if it's not a heavy leak then it's not worth worrying about. Slow-release rust protectant for the chassis. 😉
That looks like a drain plug. could it be that?
Drain plug wouldn’t be that high up. It’s on the pan.
This is NOT and drain or fill plug. You can tell by the lock nut that is an adjusting bolt for something inside the trans. Proceed at your own risk.
