The syrup is in the inner tank which isn't air tight... guess it goes bad...
Based on my experience in restaurant management and dealing
with more than a few health inspectors, I suspect that if the tank is not airtight they are worried about bacteria because all of that sugar would be fertile breeding grounds. And let's not forget about the ever popular found dead in the coin box of an old machine - - - vermin!
I would think if you could get one running it would be great for home use and parties but make sure that everything is kept very clean. Bleach water is a great sanitizer. I also would not recommend leaving syrup in the machine during long periods of non-use.
Tim