i am getting water on my floor board. i think it is the heatercore. how hard is it to replace it?

Does it smell like anti-freeze? Does it look green? Might be from your windshield too, so make sure before you go all out. Also, if it is the 'freeze then it could be either the core, or the heater core valve. The valves are notorious for developing leaks if the system has any corrosion in it. The rust and scale will chew up the seals in it.

 

Replacement *technically* requires removal of the entire dash, but there are methods that do not require the complete removal. People have cut the side off the heater core box, and slid it out from underneath then sealed it back on with silicone. Looks knarly, but you can't see it with the interrior put together anyway.

check the ultimate subaru repair manual forum.