Some places to start.
Experienced numerous leaks when I purchased my h27. Here are the things that fixed the leaks.1. Remove and rebed the forward and mid hatch. Check hatch seals and replace if necessary.2. Remove and rebed the opening ports. Also check/replace the seals on the interior opening part.3. Check/reseal the wiring coming down the mast where it enters the cabin top. This will require removing the mast... something to leave for the next haul out.4. Check/replace the fittings, clamps and hose for the forward anchor locker drain. Watch for cracked plastic fittings. While you're in the locker check the potable water fitting and hose to the tank. Remove and rebed the fitting and replace the hose if necessary. 5. Check cabin top and deck fittings such as winches, block mounts, mast mount, etc. Rebed.6. Check/replace hoses/clamps on cockpit scuppers.7. Check hoses/clamps on the pressure side of your potable water pump.A good way to find exterior leak sources is to pressurize the cabin with a leaf blower while someone uses soapy water and a mop on the deck/cabin. This will also help you spot any leaks at the deck to hull joint. You'll have seal a lot of openings with duct tape before you start. Hope these ideas help.