A block sealer is a last resort. That said, I had good luck with K & W seal on my 1947 Pontiac. Coolant was getting into the oil. I removed the cylinder head and the block was cracked around a couple of the valves (this was a flathead 6 cylinder engine with the valves in the block). I put the engine back together and used the K & W seal as directed. I ran the car another year until I could afford something better. I saw the car on the street a couple of years later. At least while I owned the car, the K & W seal kept the coolant out of the oil.