A crank shaft's seal only seals the pre mixed fuel/oil inside the powerhead, if kaput will see mixture spills around drive shaft and pan area when the power head is removed. If finding water in any of the cylinders will see a brownish coat of rust on top tip of plug. When changing new gaskets should be retorqued soon after to specs, check it's well torqued tight.
What about the cylinder head gasket, have you changed it ? that's a 32 year oldie motor. If not proper time to change it along taking advantage to clean all water paths and fully decarbon that area..
HappyBoating
