Looking at your picture it shows the electric connectors so that fitting used an external pump originally, as you say your pump is now in board, is that a change you have made or a previous owner? If you still want to replace the water inlet, I suggest you measure the original and then check the size against a new Truma or Whale inlet, without the electrics, it would be a bonus if the screw holes line up, but not a deal breaker. If you can find a suitable replacement, you need to remove the old one, clean every bit of old sealant off the van,and either fit the new one using Silkaflex or similar, although Truma do a sticky foam gasket to fit their inlet, if you are lucky the water pipe connector inside the van will be a push fit onto the new inlet.