Transformers often fail after a given 'long time', they are usually made out of many laminated plates glued together, and over time the glue will fail, plus the

Transformers often fail after a given 'long time', they are usually made out of many laminated plates glued together, and over time the glue will fail, plus they tend to vibrate at the mains frequency, which can shift things around over time and cause failure too.