Im in the process of rebuilding a 12ht at the moment and my cylinder head is at the machine shop for check up and new seals and valve grind. I got a call from them yesterday and they told that the head appears to have 6 sleeves or tubes that run horizontally through the head and several of them are rusted through and leaking coolant into the head bolt cavity. This wouldn't cause any kind of external leak but will cause coolant to get on the bolt and if water is used could cause it to rust. Several of my head bolts appeared to be a bit rusty so that explains that. I see no mention of these sleeves in the service manual or any kind of parts schematic. I emailed my favorite parts supplier in Australia and they have the tubes in stock so I have some on the way. My question is has anyone else had to replace these? I don't have any photos of them because the cylinder head shop is an hour or so away from me and I wont get down that way until I pick the head up.
