Mycoplasma is common enough and can be latent in a flock. The discharge is typical also. Stress will bring it out. I haven't heard you mention any stress, though. I would not put too much faith in the friends account of an attack. Most people would think any chicken interaction, like breeding, is violent. You can take a live bird to the necropsy lab but it won't be alive for long. They kill them and pretty much completely dismantle them. You receive a report. Bird goes in the incinerator. Trust me....you want that.