Rick: There you go again posting while I'm thinking.
Okay. Why would you buy a used sound unit in questionable condition when you've got one that works already? If you've got deep pockets and 35 dollars is worth the trouble, by all means buy it.
For $2.70 you could get a buck converter that would allow you to dial in the sweet spot for your unit. You'd hook your AC voltage to the converter, adjust the output voltage with a volt-meter, and hook it to the sound unit. I'm pretty sure that would work. Let me know what you think.