So, turn your aircond on and run it for a bit (say 10 mins)
then just feel with your hand to see if you can feel the leak on the pipe. (you should be able to reach under the glovebox)
then if its wet, pull the hose off from the aircond box, and then you should be able to pull the hose through the firewall, its only about 10cm long from memory.
then just replace it with a hose the same size....either buy a new one from Subaru, get one from a wrecker, or just tape the cuirrent one up with gaffa or electrical tape...
i would go the gaffa tape option myself
Steve.