It really depends on the extent of the rot/moisture - I had some around my chainplates and deck fills but was able to scrape it out with various tools from the openings (worst case was about 4" from the opening). I also applied a vacuum for a while to reduce the moisture content. Fill with thickened epoxy and re-drill the holes. Not a bad job, does take some time and you need decent weather. This can become a much bigger job if the rot is extensive however (many threads on how to do major deck repairs on this forum). If you haven't already, get/borrow a moisture meter and determine the extent of the moisture - if you have to cut the deck to access (from above or below), it's a bit more involved obviously. Also you want to determine if the deck still feels solid in the high moisture areas (use a brass/plastic hammer). It will be hard to find a boat that age, especially an O'Day that doesn't have some deck rot - owners need to keep on top of bedding deck hardware. The good news is that O'Day decks are cored with end-grain balsa so the moisture travels slowly. If the deck feels and sounds solid you don't have to fix it right away.
