They are very tough to get out. Gotta drill them straight to have a chance. Heat didn't seem to help me much. I put a 6mm helicoil in mine and it works fine, but - I drilled to deep and penetrated through the head. Thankfully it doesn't leak and I flushed all the metal out numerous times. If you can afford the gaskets, tgear it down and do it in a milling machine so it can be indicated in correctly. You won't evn need a helicoil if done dead on... GOOD LUCK!!
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country