Identifiy the Diode-ish device
Have you checked if they are actually diodes? I've taken apart old electronics, and seen devices in a very similar package that were just diodes.

In the early days of silicon diodes, they came in a lot of odd packages. It wouldn't surprise me if that was actually a diode. Considering that this is an older piece of equipment (googling Bruel &amp; Kjaer 2803 gets me documents from 1967), it's probably just a early silicon diode.

I would bet that the tapered end is very likely the cathode.

Try using the diode-check option on your multi-meter. They're probably just simple silicon rectifiers. If so, you can replace them with inexpensive 1N4001 diodes, or similar.