best thing is to fit a pressure tester to the system which will simulate pressure in the system to create the leak with out the heat!
as for what can leak...
starter/inlet side you have two main heater hoses coming out directly above the starter motor. one of these also has a joint directly above the starter motor as the heater control valve sits in it, these then go along behind the rocker covers and go into the heater matrix near the abs pump on the passenger side, above the exhaust down pipe area (easily visible from above)
you also have a metal tube which runs around the back of the engine connected with two smaller coolant hoses to another metal tube which runs under the plenum and to the inlet manifold.
turbo side you have a banjo which bolts directly into the block half way up which then tee's off into each turbo supplying turbo's with coolant (there is also one of these for the oil supply). then coolant then exits the turbo's and heads upwards to join the water channel which runs along the passenger side rocker cover going forward around front of the timing cover, and rearwards to the bulkhead (where you see two pipes which bolt together)
hopefully some help if u can read my sunday morning logic
