Antifreeze leak

Sounds like a bleed plug for the coolant. Did someone recently try to bleed the air out of the system?

Not that I know of. It all of a sudden started doing it. Like I pour the antifreeze In then it leaks from that bolt. I was told it could be a gasket.

I suspect failed water pump. When the shaft seal goes water runs down the front of the engine and usually exits right next to the oil filter. If your water pump is starting to growl when the engine is running, thats a good indication. But it can fail and not make any noise at all. If you can get a screwdriver behind the water pump pulley and gently pry on it. With the engine off. If it rocks or moves at all. It has failed and is likely the cause of the coolant leak.

I wouldn't pry on the water pump as the bearing is likely still good and the seal is bad, but I would try a small mirror to look at the weep hole in the water pump to see if it is dripping coolant. If coolant is coming out of the weep hole or from the bottom of the water pump then it is time for a new pump. How many miles on this Mustang?

You do realize that bearing failure is the root cause of seal failure. And you certainly will not hurt the bearing prying gently on the back of the pulley. That is the second step in diagnosing water pump failure. The first is finding a leak.

Seal failure is the root cause and bearing failure is secondary in my opinion. Over the years I have seen more seepage in water pumps caused by seal failure or corrosion than I have bearing failure. Bearing failure happens also. Telling the mechanically uneducated to pry on pulleys is asking for trouble. Again just my opinion. I WAS wrong....once.

Ok I have similar in my 94 gt. Right next to the oil filter we thought it's a coolant temperature sensor. There's a plug that pops into it. I'm not sure yet. BTW we just changed the water pump thinking that was the main issue. After New one installed we noticed it was leaking from this"sensor". Could be called something else