Hey, nice to see you back!
I'm glad you've been enjoying watching your JD grow, and I can tell you've really gotten attached to him. Sorry to hear about his recent health issues.
Unfortunately it sounds as though he has a wound which has become infected. So how do you go about treating it? Well, I'm thinking an antibiotic might do the trick. The fact that the wound appears to be draining/'oozing' on its own is good, but that alone may not be enough to prevent the spread of infection. Plus there is likely cause for concern when it comes to the other fish (also undoubtedly stressed) and the possible spread of infection.
Melafix on its own may help, and even a Melafix/Pimafix combo might work together to prevent secondary infection. But judging from your description of his symptoms, this sounds like an infection which warrants something stronger.
To be perfectly honest, treatment may not mean a whole lot if you don't get down to the root of the problem and address the causes of his illness. I'm about 99% sure that it is aggression-related, and a big factor is water quality. Even if your water quality is up to par (no ammonia, no nitrItes, nitrAtes at or below 20 PPM), a fish which is injured in the presence of aggressive tankmates will typically have a tougher time recovering than a fish in the same conditions with no aggressive tankmates. Why? One word...stress.
You already mentioned how your peacock was killed.
Based on your stocklist in this particular tank...
1 yellow lab
1 kennyi
1 livingstoni
1 jack dempsey
1 common pleco
...I'd be willing to bet that the lab will be the next victim (assuming of course that your JD is able to overcome his current health issues).
I'm sure SinisterKisses and others could comment more accurately with regards to the compatibility of those Africans. Based on my understanding, kennyi are extremely aggressive, labs are wusses, and livingstoni get pretty big. JD can get to be pretty big as well, so you're looking at 3 'potential' (I don't know the current size of all of your fish) brutes in a tank which does not offer much in the way of swimming space.
Lotus would probably be the one to ask about what specific types of antibiotics you ought to look into, but I'd say you really need to work out the other aforementioned issues if you truly want to solve the problems once and for all. One last note on the meds, in case you don't hear from Lotus right away...I'd probably check out what's available in your area first and see if you can get your hands on Maracyn and Maracyn II.
Hope this helps get you on the right track.
BV