Replacing exhaust elbows question

[markloos]

I rec'vd two Merc elbows that shipped with gaskets for twin 4.3/LX engines. The gaskets had two slots that were cut out right where the coolant (closed system) is chambered. I attached the elbows and when filling with new coolant, I realized that I had more than 7 gallons added to a six cylinder engine and it was still not topped off. I spoke to a mechanic who said that the gaskets were probably made for the original specs when the boat (1995) 290 Sundancer was built and later on SeaRay or Merc decided to add an aftermarket Heat Exchanger....which requires the gaskets to be solid with no cut outs. THe mechanic said that I was pouring in my coolant and it was just mixing with the sea water because of the gaskets and I need different gaskets.

Question: Is the diagnosis correct? If so, how could Merc ship out wrong gaskets or was there somewhere else I should have checked first before installing these elbows.

Any input on this would be helpful.:smt024