How old the vechicle is not the only factor. Type of driving (highway/city) and how many miles on the vechicle also matters. They recommend 5 years or 60,000 miles to replace timing belt and at 5 years or 78,000 miles for your spark plugs.
RepairPal Certified shops can diagnose and repair your 2008 Mercedes-Benz ML550. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.