It is crucial that the organizational culture reward employees for making this happen. When you think about it, a lot of corporate cultures reward the opposite

It is crucial that the organizational culture reward employees for making this happen. When you think about it, a lot of corporate cultures reward the opposite -- employees hoarding key knowledge so they can use it to their advantage. To do this, avoid creating a culture that fosters rivalries. I know it's controversial to say this, as many business people seem to think that brutal rivalries are what leads to over the top effort. Instead, think about the knowledge as processes, and figure out how to best codify and execute those processes. If you arrive at a step in the process that appears to be something that can only be done by one person, or by a person who is leaving, that is a clue that someone is withholding information or trying to use it to his/her advantage. Nothing is that complicated, just break it down into simpler steps. Then, when it comes to onboarding, introduce whichever processes make the most sense for the new hire, and encourage him/her to view them both as an example of excellence but also as something that can be improved. Doing this helps the new hire understand the design perspective behind the processes, which is preferable to following them by rote (which is surprisingly common even among otherwise bright people). It sounds from the question that you have a bit of drama going on, so you may actually want to sketch out the processes as you think they are and then incentivize the team to make them all precise.