(1) could be head gasket, cracked block, ????
(2) Head gaskets as they are made today are usually replaced. The flatness of the head should be checked if the head gasket is blown and if need be it can be ground flat.
(3) Often the valves remain on the head but not always.
(4) just generaly take care.. a universal mechanic may have specific warnings.
I think Universal may be a division of Westerbeke.
I saw parts and manuals listed.
Purchase a service/repair manual and a parts list, they are invaluable in doing repair/diagnosis.
However, any good mechanic should be able to help you determine the cause. If it is a cracked block from winter freeze etc, then you may not want to bother purchasing the manuals which will likley be $50 to $75. If it is just a head gasket and you do the work yourself, my SWAG (guess) would be (a) manuals: $60, (b) Gaskets: $75, (c) machine head flat (if needed) $100, (d) box of bandaids/ bottle of aspirin (generic) $5