I got a single casting from PRC to replace a damaged one, and the hole is plugged with some sort of plug. The threaded hole is still there, but the water passage is plugged off. Should I not worry about it or try to get it opened up? I bolted the heads on already so it's facing the front where it's plugged. Looks like you can drill it, I rwead one post where a guy said he drilled it, but it looks a bit sketchy.