[Rick Parker]

I agree with Ex to avoid removing the threaded core plug. They exert a certain amount of stress on the cylinder walls and if they were originally "Torqued to spec" when the engine was built, it may be difficult to duplicate at this time, especially considering the difficulty in accessing it on an installed engine(?). GM dealers have in their parts depts some brown pellets about 1" in diameter and 3/4" thick that are made of some sort of sealer for the cooling system. It is common practice while replacing intake manifolds or heads to toss a couple of these pellets in the cooling system to eliminate any minor leaks that could develop after the job is completed. I have used them in the past. They are easy to administer, nothing to spill and work well. I too would recommend retorqing each of the heads.