Yeara ago, I had a 1947 Pontiac with a flathead 6. Coolant was getting into the oil. Pullingll the cylinder head revealed that the block was cracked around one of the valves. I put the head back on with a new gasket and bought a can od K & W seal
I drove quite a few miles after that with no problems. I traded the car and it was still on the street two years later. I don’t know if that product is still around, but it worked for me.