Glad I decided to replace my manifolds!

[further]

I was very close to just replacing the gaskets between the manifolds and elbows, but decided since it’s a new to me boat (relatively speaking) I’d just replace them and be safe. Glad I did. Lots of hidden rust up against the block on the starboard side. Also there was what looks like a bit of water/guck in one of the chambers on the port manifold (which wasn’t nearly as rusty as the starboard side). What would cause this? Where from? I looked inside the motor and there is no moisture in that corresponding chamber and there is very little rust inside... Anything else I should do aside from replacing with new?

 

[RobRoller]

Most likely that water/gunk ran down the exhaust when you separated the upper manifold from the lower. Honestly most of that rust and corrosion is superficial on your manifolds that I can see from your pictures and would have been fine to run. That being said, $1k in maintenance prevention can be worth it for time lost on the lake due to overheating etc later.