1.0-litre Peugeot 108 and the equivalent Citroen C1 and Toyota Aygo of this generation are fitted with the Toyota 1KR-FE engine, designed by the Toyota subsidiary Daihatsu and generally speaking have proven to be a reliable engine. However, the most common issue tends to be high oil consumption caused by worn piston rings or valve stem seals and carbon build up in the intake caused by the EGR system. If your garage has diagnosed chain guide issues then resolving this would require replacement of the guides and likely the timing chain itself, which is typically quite an expensive job, but we would suggest shopping around and trying other Peugeot/Toyota independent specialists for other quotes. As with any engine, regular maintenance, in particular oil changes are essentially for longevity.