To cull or not to cull my flock?

I have a free range flock 20-30 hens of all sorts of breeds and ages. 10 days ago I purchased 8 pullets around 16 weeks (all seemed health). This was my first time to purchase pullets and not day old hatchery chicks. Every year I order a few chicks do to a small loss being free range. This year I wasn't in the mood to do a brooder, so I thought( past tense) the 16 week pullets were a great option. Anyways 3 days ago one of my wyandottes ( a little over a year old) started sounding funny. I thought she maybe just had something stuck on her throat, I wasn't sure, but wasn't concerned chickens are weird little creatures so I laughted and moved on. Last night I put my ladies to hex and could hear some gurgling (rales) from a couple of them. This morning about 3/4 of my original flock is coughing sneezing, gurgly and low egg production. One even has puffy sinuses all a perfect match to Mycoplasma Gallisepticum Infection. All the symptoms match, the incubation time matches, and non of the new pullets have symptoms. I don't breed my chickens I don't sell them I just have them for eggs and entertainment. I seem to read mixed reviews on what is the appropriate action do to the fact that they will all be carriers for the rest of their lives. Any advise would be great! Thank you, kathryn