The company that made the original heaters is no longer in business, but I was able to find, with the help of other Newell friends, a suitable replacement called the King PAW (PAW standing for Pick A Watt). It comes set up as a 1500 watt heater, but you can disconnect individual heating elements to reduce the wattage depending on the size of the space you wish to heat. I elected to disconnect the 500 watt heating element to reduce the wattage to 1000 for the water bay as that is what the prior heater was set at.
I waited for a day off to install the final heater, because just as with the first two it was necessary to make the opening in the heater box a few inches larger to accommodate the slightly larger dimensions of the King PAW, and the area where this heater is installed is quite tight. In other words, I wanted as much time as would be needed to get it done right with no rushing around.