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Sound like progress to me! The next step is to measure the terminal voltages again and compare them to the expected values.
The audio is applied to the final stage through R16 into the base of Q3 thence to Q2 and then to the emitters of Q4 and Q5. Before condemning these components, do the voltage check.
Also be aware that my experience with this transmitter has shown that an improper antenna load can cause the audio to be distorted. According to my information, this transmitter “expects” to see a load of about 800 ohms resistive. If you are testing with a wire antenna, are you doing so with R18 installed? My transmitter audio was terrible on bench test with R18 removed but cleaned up to perfection with it installed.
You are now in a difficult phase of troubleshooting unless the voltage checks turn up something. I don’t recommend a shotgun replacement of all the transistors until you have more data.