Check it out carefully to be sure where it is leaking from. If it is a leaking core plug, and the truck is your daily driver, you may as well go ahead and yank the engine now and replace all of them. If you try and go with Stop Leak or something, it will probably be a temporary fix. And the plug will still blow a hole in it, but when it is 95* and your a/c is ripping you'll be on the side of the road. May as well do it now before the weather gets too hot.