I have a detroit 12.7 series 60 with close to 1 million miles on it. It is now starting to heat up on long pulls and now the heat isn't working. I took it to a few mechanics and they are saying either a cracked head or a cracked liner. The cheapeast estimate i got was around $13,500. That included overhaul and head, bull gear, and cut counterbores and install sleeves. Now is this what they mean buy a complete overhaul, or is this just a bottom rebuild, or a top rebuild? And after i do this overhaul, will i have to go inside this engine again anytime soon?