You must be dealing with a mild strain of MG. Since you are familiar with the disease, you must know that your birds are carriers because they have survived the disease.Hi there!
My flock has MG. It was really bad the first time around for 2/6 of the chickens. They pulled through. I gave them coilloidal silver and Tylan. I can't say I would use those again because I never saw a relief in symptoms. I isolated the worst one and had to pretty much force feed her and give her water. The other chickens barely showed symptoms, I just knew they weren't feeling 100%.
They are all happy now. I found that letting them free range vs isolation was best for my flock, especially if symptoms come back. Much like humans, doing what they love to do helped. Even when they didn't feel good, walking outside and sitting under bushes seemed to do them good. I know everyone says to cull the flock, but ours is so small I just didn't see the need. I won't sell them because I would hate for another person to go through the stress we went through.
Overall, egg production and quality was not impacted at all. I get eggs daily. The hens didn't lay for about a month after they had their first round of symptoms, but that is it. Our rooster doesn't seem to mate as much and he pretty much always has a little bit of eye crusties but he crows and runs around our property with no problems, happy as can be. So, culling is a personal decision. Just wanted you to know that MG doesn't have to be the end.
Also, when I know periods of stress will be coming up (extreme temps, new flock members) I give everyone some nutridrench in their water.
You mentioned "new flock members." Not only will there be periods of stress coming up with new flock members, your carrier birds will be infecting the new members if they are mixed together.
If you're going to get new healthy birds, I highly recommend that you build a coop/pen a good distance away from the existing infected flock and practice strict biosecurity; including but not limited to changing clothes and shoes, practicing personal hygiene as not to infect the new birds. Ensure feeders and waterers are not cross contaminated.
You're looking at ongoing quarantining of a new flock away from sick birds.