would water not just piss out the coreplug hole if it had fallen out an not the cam cover ? the coreplugs on the block should all be able to be checked and replaced with the engine in the car but im not sure on where all the plugs are on these engines. there in some pretty stupid places on some engines lol. i know that you havent but just so ya know you should never rely on core plugs or freeze plugs to save you from freeze damage hope your engines alright bud and that ya dont get temps like we have here at the mo -14 because that wont help much Russell