I have had a cracked 205 block, As said, it drove fine unless you gave it real stick for a prolonged period, then the temp used to rise and it used to use a fair bit of water. Didn't realize the block was cracked until my mate broke the car . But it was a 205 block using genuine cosworth head bolts with a cometic MLS head gasket, I always put the water loss down to that. It had cracked across the headbolt holes on the section between no1 and no2 cylinders, and no 2 and no3 section, cracks were hard to spot, on both sides of the block .

Hence now I would not EVER consider building a high power YB around anything other than a long studded 200 block, people will disagree but I have yet to see or hear of one of those failing