OK. Back to basics.
Where from?
Run the car with the bonnet open, and you looking.
Wait until the fan kicks in and the thermostat opens so the coolant in circulating everywhere.
Place some newspaper under the car so it covers the entire engine bay.
This will help you to identify spray/drips from below.
Set the heater controls to hot.
With the engine running squeeze and manipulate the pipes at the joins with the jubilee clips/clamps. Know failure points due to degradation.
Lift the carpets in both footwells to check for leaks from the heater matrix.
Basically, look for spray, and listen for hisses.
Jonathan.
