Using 230V-115V Transformer for 240V supply
You're talking about that step-down transformer you bought. 

Step-down transformers are designed to turn a 230V Euro-style supply into a 120V North American style output.  They are designed to do this all day, all night, for as long as the device lasts. 

The life of the device will be decided by its build quality.  Is a General Electric product better than a brand-you've-never-heard-of East Asian made cheapie?  Oh, you bet it is.  Still, a transformer has no moving parts, so expecting long life is reasonable.