Hull / Deck join
Pylons where they go through the deck
All fittings screwed in the transom (gudgeons, drain plug housing)

Lightly pressurize the hull using a shop vac set to blow. I've done this in the past by using the crevice tool and just hanging the tip of it in the drain plug opening while the hose is loosely taped below the rudder. Allow excess air to blow out of the hull past the vaccuum hose. DO NOT DIRECTLY CONNECT THE VACCUUM TO THE DRAIN PLUG! DO NOT USE AN AIR COMPRESSOR! It's suprisingly easy to explode a hull. I've seen the aftermath - which is non-repairaple.

Once you've got your pressure system going, use soapy water on all the suspect areas. If it leaks, you'll see bubbles or you'll hear and/or smell the leak.