Leaks often don’t originate from an obvious spot. That drip onto the forward berth (and its always right where you like to lay your head, isn’t it?) may be coming from a radar arch fastening 10 feet away. While there are many ways to find the source, here is one way that works most of the time—provided your willing to put in the effort.
Close off the cabin, dogging down all hatches and ports. Wedge a shop vacuum hose into the companionway door or any one hatch and seal off the resulting opening with plastic sheet and packing tape. Station a helper inside the cabin before sealing it off.
Now turn on the vacuum and liberally apply soap suds all over the cabin. When bubbles are spotted belowdecks, you’ve found your leak.
For larger cabins you may want to seal off the cabin in sections, moving from stateroom to salon to head and so on, until the leak is found.