yes, its more than likely that its a heater core.

 

my heat works fine and if it is the heater core cant you smell some antifreeze?

 

+1. Do you have a/c?

that drain gets clogged because of leaves and debris.

 

yes i have AC and where is the condensation drain?

 

My AC has been a 10 yr 'chase' to find freon gas leaks. When my heater core started leaking, I replaced it. when I had the dash and heater box out, I also replaced the evaporator core to eliminate it as a source of slow freon leaks. The final fix was replacing the black o-rings with green ones for R134A.
Now about your water leak, the grommet where the A/C water drain is (between the Heater box and the firewall) has a "lip" that has to be pushed through the firewall hole. I was working alone and the "lip" ended up pressed up against the firewall from the inside. Once I got the A/C working well, the water dripping out of the drain went mostly inside the car vs dripping on the ground. I had a lake in the passenger side floor pan during a long trip out west. Not wanting to pull the heater box out to get the "lip" pulled through, I put on a brass 1/4" brass elbow into the drain hole. Put a little teflon tape on the threaded side and installed a hose on the ribbed end (set up for a hose.) Routed the hose down and tied it to tie banded it to the frame on the pass side. No more water leak, good A/C and good heat. Enjoy!!

 

We don't like zombie threads either. Back from the dead for the 100th time today!

 

Pretty sure he has it figured out by now, if not after 8 years of leaking water onto the floor I suspect it is draining out the rusty hole in the floor board.