[grandinj]

If you repair it yourself, you have more flexibility in terms of replacing spares with newer items i.e. replacing a whole module when it a part of that module becomes hard to come by.

Internal documentation ..... hmmmm.... LOL.... Often not, word of mouth is the rule.

If there is internal documentation, it's generally pretty rough. Getting it to the point where you can hand it to external parties is a lot of work.