Are the heater pipes connected or just plugged up? If its plugged up it might be cause it leaks.
You could change the heater core or just see if its the copper pipes that go through the firewall thats leaking. They are easily changeable if they are the reason it leaks.
Its not too hard and is way easier than taking the whole dash out to get to the box. Feel free to check out the last pages of my Lolla thread (Link below) if that helps, as I sorted a similar problem out before I traded the car in.