Engine problems(valves) with ford fusion

My brother owns a 2003 ford fusion(1.4, petrol) and the valves had to be replaced last year at a cost of 1,000 euros to him, ie, just outside the 3 year warranty. Now they are gone again at a similar cost to him. Should ford not be responsible for the cost as the mechanic who repaired the car has heard that this is a common problem with the model. Car was bought from new in ireland