NavList:

I suspect that at least part of the problem is that the  cement that holds together the two elements of the achromatic objective lens has shrunk. If it can be removed from its cell(I'm not about to try on mine), soaking in acetone overnight may allow the two elements to be slid apart and the opposing surfaces cleaned of old cement. The old cement can then be replaced by a drop of Araldite Ultra-clear epoxy glue, whose refractive index is practically the same as the original Canada balsam. The two elements are then slid against each other until all air bubbles have been removed. It worked for me years ago, but I cannot remember on which sextant telescope I used it on.

Bill Morris

St Heliers

Auckland