Brass (?) staining the woodwork

It looks as though the brass is undergoing dezincification with the formation of zinc oxide, which then degrades the wood. If you want to retain the varnished finish, perhaps consider replacing the screws with bronze. The wood may respond to oxalic acid solution to bleach away the staining. Painting will require cleaning the screwheads, priming with a special metals primer and then a paint system. It may be worth considering where the moisture originates from as the amount of corrosion seems unusual for a boat interior.
 
Replace screws with stainless and screw caps or decorative wood covers under the heads to cover the damaged wood. If you can't hide something, make a feature of it.

Oxalic acid may help, I use Bar Keepers Friend cleaner mixed to a paste and left on overnight but loose the brass screw first as the acid will make it worse.
 
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I'd find and fix the leak first. There seems to be further water damage where wood meets edging strip.

Brass simply doesn't do this sort of thing without the presence of salt water or some other contaminant (wet acid fumes?) Has the area been wetted by crew with wet oilies? Or kids after jumping in? Dare you lick test? ;-0 Is there a window leak down the back of the panel?

Unlikely, but maybe very contaminated when manufactured, e.g. screw covered in salt - pull it, clean up and replace with a different one.
 
A lot of mine have done this, where possible the wood removed, c/sinks cleaned up, revarnished, screws replaced with stainless. Brass screws often break when trying to remove. Some replaced with stainless cup washers & screws to make a feature and easier for regular access.
 
All of the brass screws at floor level in my 40 year old boat look like that. I suspect it was neglected at some point and the bilges filled with water. Half of them break when I try to remove them and drilling out causes more damage than its worth.

Hopefully your dezincified brass screw is an isolated incident, but take it as a warning that the moisture content of the wood might be high, not just that water has dripped onto the screw. You should remove the screw (the tarnish will return to the wood if you don't) and see if only the head is corroded or the whole length of the screw. If it breaks then assume that the whole length was corroded and the wood is suffering from a high moisture level, which needs taking seriously.

That sounds a bit alarmist. My apologies but brass screws and damp wood holds bad memories for me!
 
Thanks for all this helpful info. I suspect that the moisture is simply long term exposure, they have been there for 37 years, and we have not had water in. I'll replace with stainless & see what can be done with the wood. It is nice have 'teak & brass' but time is limited & we got this boat to sail it.....
 
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