Victor,
The heater has a plastic bleeder screw that fails.  As long as you have
a mess you might want to start it up and visual verify what's leaking. 
I super glued the bleeder screw back together while the replacement was
enroute.  I had to clean up the mess twice because when I put the new
screw in coolant went every where.  You might want to make sure your
system is not pressurized when replacing the bleeder screw.  Good Luck.
Neal