Fixing Moto Speaker/Mics

[Mr.X]

I have a lot of Motorola HMN9026C Speaker/Mics that I'm using with my DTR radios.

All are different in terms of volume level and clarity. I'm wondering what "wears out" in these spkr/mics, whether it's the speaker itself or some of the circuitry inside?

Also, I'm wondering if anyone has ever tried a different speaker in this spkr/mic that might be a little louder? The radio on it's own goes really loud, but the speaker/mics do not, even brand-new ones.

Thanks in advance for any and all help!