Hello Val -
  Your water leak might not be the heater core; just two weeks ago the heater 
  control valve failed and leaked on the passenger side footwell carpet of my 
  '57 300C.  The heater box will likely have to be removed to get to either 
  the valve or the heater core, so it's a good opportunity to check BOTH 
  potential sources of water leakage.  The heater valve repair is quick and 
  relatively painless ($85 - see my posts from just last week about where to 
  send it), whereas I bet the heater core removal and repair will end up costing 
  quadruple that!  A good radiator shop should be able to repair the heater 
  core (if it's not too eaten up with corrosion); after all, it is indeed just a 
  miniature radiator!  Good time to replace all the hoses and clamps, 
  too.
  Ray Melton
  
    
    
    
      Greetings all,
                           
    I am sure mine is leaking as I feel wetness on the front passenger carpet. 
    Where might a new one be found or can it possibly be repaired ? I assume you 
    remove the heater box on the firewall for access ? Appreciate any help 
    !
    
    
                                                                                       
    Thanks,
    
                                                                                       
    Val Jeffers