I have an abundant supply of lemon balm. Tried it and it didn't work in my case.
And that is the problem with treating for any respirator illness, there are so many strains. Those of use with many rabbits might not have or want to take the time and expense it takes to figure out which illness it really is, and treat an animal for the rest of it's life, with the possibility of trying many things and not having them work, or possibly risking the entire herd. Though, exposing the herd and seeing who dies and who doesn't would be a quick and dirty way to see who is resistant. That doesn't seem right, but that's what you're doing if you keep an ill rabbit with a communicable disease, even if it seems mild. Rabbit Russian Roulette.
It might seem crude, but a couple hundred dollars of vet bills for a $40 rabbit, or wiping out a herd worth $$$$ and 3 years of work for one rabbit doesn't work for me. The best way to breed for resistance is to cull those that show signs and keep those that don't. My rabbits get exposed to enough germs that I am not keeping a totally sterile barn, but if they were going to get sick, they would have by now. Still I try to protect them when I can.
You have to count the cost and see what works for you. I tried for several months and still came to the same conclusion. I've culled for less than that.