I’d bet you big money it is not the block. The only way to get combustion chamber pressure into the water is from the combustion camber and the only part of the block involved in that process is the cylinder. Cracked cylinder sleeves just don’t happen unless your piston goes and a rod shoves through the side of the cylinder. You wouldn’t be driving anywhere then. Since you are not getting water in the oil (yet) the motor is probably undamaged (unless you let it overheat constantly).

You’re probably seeing radiator repair goo or maybe the prior owner never flushed the radiator. Also water sediments can really look nasty. I imagine exposing cylinder gasses to antifreeze would probably goo up things too.

Sounds like you want a new car but you might get you old one fixed before you sell it, you’d get more money that way. I’d offer to buy your old one but am about 5k miles away. It would also be a wet drive.