Anchor Light Bulb on the 4788
Finding the correct replacement anchor light bulb online is actually non trivial. I walked over to West Marine and happened upon the correct one. For my own memory and the world the information on the bulb is:
Double Index Marine Bulb
Model Number 4810834 (Which I think is West's number)
Now that I know the correct bulb I might opt for an LED in the future. This bulb cost me $17 in the retail store.