Questions about Heater Core on 5kcst

[ang@indiana.edu]

Dear Audi enthusiasts,

After I finished up my cooling system project last month, I felt much better 
than ever. Unfortunately, few weeks ago I noticed that my car started leaking 
coolant again. But this time was very special, I think, I've found that the 
coolant was leaking underneath of the Heater Unit, the air box, but it only 
when the car cooled down. Also it's leaking slowly too. So, my questions are :

1)Is that means my heater core is broken? Since there are no other things 
  inside the Heater Unit will leaking coolant.

2)Does the heater core broke easily? 'cauz I replace the heater core six 
  mohtns ago in San Francisco before I moved to Indiana.

3)How hard it will be if I want to replace the heater core by myself? 


Could any one be kind to give me some suggestions about this problem?
I'm tired to see any coolant leaking again.


Thank you 
          very much


Albert Ng
ang@indiana.edu