I was redoing my water pump gasket on my 1990 Pontiac Bonneville with 325K and I had a hard time getting one of the bolts out because the threads are bad. So I tried chasing it with a tap and the stupid cheap tap broke off immediately inside the block. I had the correct size. It broke off at an awkward slant and didnt know if it was possible to get it out of the block. Its so far in that even taking the timing cover off would not expose it. I'm at a loss. Would hate to junk the car over something stupid when it was driving fine asides the leak.
If your block is aluminum, then you can use a solution of Aluminum Sulphate. It's sold in some food stores as a food additive called "alum powder". It dissolves steel, but won't touch aluminum, but it could take some time. You'll have to get creative to find a way to keep the solution inside horizontal holes though. Some putty and drink bottle or something.
