Only had boat two years never pulled them notice water stain on both sides but really saw-water leaking for the first time after checking it while under pressure leaving marina
Both my manifolds had small holes rusted through the risers, the gaskets were still good. Don't leave it too long as water leaking into the cylinders via the exhaust manifolds can be very expensive to fix!
Pull the risers like everyone else says. I use a flat file to deck the surfaces after you remove the gaskets. Dont forget to use anti seize on the bolt threads when reinstalling them.
Turns out it was a bad gasket so I replaced both to bad I didn't know about anti seize if it would had helped I was toqueing the bolts as bad luck would have it snaped one but the sun was shinning an when I took it back off the broken part of the bolt backed with no problem Their is a God