Re: manifolds
Don't make the same mistake I did and live in denial about the possible condition of your mainfolds. I now have a dead engine as a result on not checking mine after owning the boat for 5 years and not knowing the complete history of it's use. ie. salt.vs fresh water.
I noticed a slight overheat issue the past few trips and observed a small rust staining on the outside of the mainfold where water had trickled at some point.
Well the short story is a leaking manifold that pumped sea water into the #4 cylinder then #3 and before I realized it had sewater contaiminated oil. I pulled it out of the water immediately and flushed it with fresh oil so hopefully have saved it enough to be able to rebuild it.
Bite the bullet and check and buy the manifold/riser if needed, it might save you the cost of a tota

l rebuild!!!