If you are the only guy who knows all the opaque rules of an important business system you have incompetent management and they should be replaced. Single point of failure and all that. What happens when you are ill/away and a critical bug must be fixed, or a critical system goes down and must be restored?

I predict a lot of pizza's boxes around the office. And you working remotely like mad while ill or from the beach/sky resort. A lot of screaming, too. :)