Unfortunately surviving birds with a respiratory disease become carriers for life despite antibiotic treatments. Whatever respiratory disease a bird has, will eventually build resistance to the antibiotic that has been given to the bird. More powerful antibiotics will be required...on and on it goes until there's nothing that will treat the disease. Then if it's a viral disease, antibiotics are ineffective. If your rooster has had a respiratory disease as you mentioned and has been free roaming in your flock, it's highly likely other birds have been infected as well and other birds would have been showing respiratory disease symptoms. Have your other birds been showing respiratory disease symptoms? If not, your rooster may have a fungal problem.
If it's bacterial; lay your rooster on his side and snugly wrap a towel around him, and lay him on one side on a table. Use an eyedropperful of hydrogen peroxide to loosen and boil up gunk/debris in his ear. Then use a q-tip to slowly and gently clean out his ear. You will have remove some of the cotton on the tip of the q-tip in order for it to fit inside his ear canal. Do NOT put the q-tip deep into the ear canal. The hydrogen peroxide will have released and lifted most of the gunk making it easy for you to swab the ear canal. Use as many q-tips as necessary to clean the ear canal. Next, use Neosporin ointment to fill the ear canal, simply put the tip of the tube into the ear canal and squeeze it until the ear canal is filled with the ointment. Then flip him over and get to work on his other ear, same procedure. If ear mites are involved, the Neosporin ointment will smother them to death. Once you release your rooster, he might shake his head for awhile, this is normal. You will most likely have to repeat the ear cleaning 2 or 3 times a year. You can give him tylan 50 injectable orally; 1/2cc once a day for 5 days but no more than 7 days.