Generally RonD would be correct but on the 3.0's the gaskets tend to leak on the outside of the passages for the water pump mine leaked and was completely sealed between where the oil lubricates the chain and the portion that passes coolant to and from the pump. Also it is a very common problem on the motors also the one bolt you speak of is i assume the top left bolt that goes through the pump and cover into the block and actually three bolts on that side go all the way to the water jacket and can leak. Its possible to reseal those bolts individually but as stated if the gasket is damaged and continues on unattended it can eventually break down to the point where it leaks in the oil. In my opinion if you have basic tools and a saturday its a good idea to swap it if you suspect its leaking considering its a common issue. Cost me $100 in parts including a new water pump and about 8 hours total but i worked off and on over a weekend to do it
New DD-2009 Ford Mustang GT/CS candy apple red.
(sold)2003 XLT Tan 3.0L V6 5-speed, Lots of mods.