I have here two Motorola MX3013, what is some kind of German police radio version of the Saber III / MX3000, VHF low, 75 MHz band. Now one out of 1991 performed just fine, while on the radio from 1994 TX audio was low and muffled. Alignment just fine, so I thought, maybe the mic. Replaced the mic, no change
So I thought, maybe a broken C or R or something, hard to find without service manual, you have to live with it. The radio was usable and all, just had to talk a bit louder when TXing 
Two or three years later (just half an hour ago) I decided to have a closer look again, and I found that directly to the Mic connector on the main PCB some parts were missing on the 1994 radio. It was the circuit of a simple mic preamp, one transistor, two resistors, one capacitor, and the whole thing was missing and bridged with a 0 ohms R.
So I inserted a transistor, soldered the 10k and 4k7 Rs in place, also the 100nF cap - and that was it, identical mic sensitivity!
Now why did they change this? Is this generally known for those radios, or was it a special mod for German police, maybe for highly noisy environment?
Thank you for your ideas