it is months since I posted my problem, but it was indeed microplasma and the tylan did the trick!
I still have the original 4 chickens I started with six years ago, and the other 4 which makes up my flock are now four and three years old. I get from two to five eggs a day in summer, but only...
I think you will find this is' mycoplasma', it is highly infectious, but quite easy to cure with Tylan antibiotics. It is similar to pnemonia in humans, hence the wheezing lungs.
Quick treatment is always important.
I do hope recovery is speedy.