A fellow in the Unertl group took it upon himself to take his 15X Unertl varmint scope apart. Not something any of the various John Unertl recommended you do. Though oddly enough a lot of the Unertl was designed to be field serviceable.

Common things of the day would have been fogging, water getting into the optic and broken crosshairs. It is very simple ( not so simple for current generations though) to fix all three of these problems in the field,

The scopes are very tough and almost foolproof. Or at least they were in the day when everyone used the correct mounting bases etc. A lot of knowledge on the old externally adjustable scopes and their care and adjustment has been lost to time. I hope I am slowing that loss of knowledge down some what here.