When I was a vice president at a large bank, I had a team that was responsible for production support for an online corporate banking application. We had 1 or 2 people on the team who were experts (with years of experience supporting the application), while the other members were inexperienced.
We found that the inexperienced people kept asking the 2 experienced people for help, and they were tremendously overworked.
As a solution, we created a very simple, informal wiki that was only accessible to the group. Then, after every incident where a junior member needed assistance, they created a quick note with key words on how it was solved. Also, whenever the senior people solved a problem on their own that they thought might be hard for the junior members, they took a few minutes after solving the problem to write up a quick note with key words.
The key was that we didn't mandate a format or make it complex. The support people were busy and did not have the bandwidth to either write a document, or read through one. It had to be a quick and dirty note, or else it wouldn't get done and/or wouldn't be used.
The result was that, in about a month, we had an expert reference system that reduced the junior's need for senior support by 80%.
My advice is that I've seen many internal documentation systems at companies that are not updated and aren't used, because they are too complex. Teams need the ability to share quick and dirty notes that can be quickly created and quickly accessed.