Mercruiser 5.7 V8 Engine Water Leak - Headbolt Sealing & Repair

Question
Hi, Another question.

The mercruiser engine which I have has been rebuilt.

The engine is letting in water which I assume is coming due to the fact that I
did not seal the headbolts.

Can you tell me what type of silicone I should use to seal the headbolts or am
I missing something.
My only other thought is that the headbolts should have a rubber jacket
which seals them when tightened.

Can you shed any light on the subject

Many thanks  

Answer
Steve...A number of new products hit the shelves each year, and some are better than others. Best you consult a marina or two to determine which one is more frequently recommended. Are you certain it's the head bolts, or could it be a defective head gasket?

Safe Boating
Ron