I have a leak coming from the rear pass. side of the head. from under the truck i see a hole near the corner of the head. it looks to be about 3/8 in dia. there is rust in it and can't tell if there was a plug in it or if the head was made that way and the wall is just rusted away. anyone have an idea if i just blew a plug or what? thanks. 1999 5.9

 

I'm going to gamble a guess it is a freeze plug. I got to admit the cummins block is full of them...

 

that's what it was. i got it out, but the trick will be to get one back in. thanks for the reply.

 

I have the same issue. What size of plug did you end up using?