Sea cock

It does look like a crack. If it is, you need to pull the boat ASAP and have the valve replaced. If it splits or opens up, the boat will sink or at least fill with water to the gunnels.
Get them all replaced while you are at it.
 
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It does look like a crack. If it is, you need to pull the boat ASAP and have the valve replaced. If it splits or opens up, the boat will sink or at least fill with water to the gunnels.
Get them all replaced while you are at it.
The boat is out of the water now I have to fix it
 
You can use some Zep Mold and Mildew cleaner liberally down there and then wash it out the aft plug to get a good clean look at it.
 
Me, I would replace it anyway. Does not cost too much, one less thing to worry about.