Damaged Borgs.

[Sir Stabby]

Borgs are un-repairable, both using the docking stations and welder/wires. I was definitely damaged (I was just fighting a giant evil drone in arrivals), and this has happened to me in the past too. All roboticists I have talked to also said that they have encountered this problem.
1. Damage yourself.
2. Attempt to repair.

[Paineframe]

Rather than that, it seems like borg damage is in some weird limbo state where it's neither there nor not there - after taking some damage, borgs will sometimes have damage visible on examination (dents, sparking wires, etc), but they'll show up in the status window and the docking station as undamaged, and attempts to repair them fail. It doesn't always happen, and I'm not sure exactly what goes into reproducing it.

[Zamujasa]

Borgs have two health metrics; the one that shows up in the Panel window (e.g. "Head Unit Damaged (33.3333%, 33.3333%)") and the generic one that other things (e.g. humans) use.

The health icon in the top right runs off the second one, which is why it will change whenever you get hit by a critter or otherwise take damage, even if your panel window doesn't actually show it.

Use a health analyzer to view your secondary health. (This also seems to work on floor tiles and maybe other things ) As for healing that sort of damage, it might only be doable with targeted welding/cabling outside of a docking station?

[Spy_Guy]

It's a holdover from the olden days of borg damage. You can't repair it, unfortunately.