We have had water there on our 260 as well. I discovered it was flowing in from the hole bored near the aft end of the cabinet for wire runs from the batteries, motor, etc. to the breaker panel. The water was flowing from the bilge area under the aft berth while the boat was heeled to starboard. The water actually originated from the centerboard trunk under the compression post while the boat is under sail and heeled excessively. It flows across the top of the ballast tank and aft to the bilge area. I've observed this happen, but still have not traced the actual intrusion source. I believe it may be the joint formed by the compression post and the cup on top of the trunk (this area has been wet on occasion). I've also seen it fill the compartment aft of the head sink while on a port tack, but it dissipates fully from this after an opposing tack. I know its not a ballast tank leak because it would have a strong smell. Hope this helps. George's link is full of great information as well.