AO Spencer binocular head repair

Hello,

I recently purchased a used AO Spencer binocular compound microscope (model #
unknown). The interpupillary distance adjustment works smoothly, but the left slide
that the eyepiece attaches to is loose. The result is double vision if it isn't held
up manually. Does anyone know of an adjustment, or some way of shimming this
mechanism to tighten it up? Or maybe a web page that could give me a clue for
repairing. For now duct tape will have to do.

Thanks,
Dave
.