My 1987 mercruiser stopped suddenly. I tok off the alternator as it failed to turn. I replaced it. Still no luck starteing. Several people have told me it sounds like something else seized up. I trid to turn the crankshaft with a breaker bar. No luck. I was told to remove the plugs and try. As I was removing the wires I noticed a big crack on the side of the engine with rusted water dripping down the ide. Do I need a new engine? it is a v8 260 h.p.