I bought my 2008 Tribeca in January 2014. It only had 26,000 miles on it and looked new. I don't know the service history. I had the 30,000 maintenance done on it right after I bought it. It is now 7 years old. Given the low millage, should I be having the maintenance done based on age, rather than millage? For example, the spark plugs should be changed at 60,000 miles. Should I go ahead and have them changed since the vehicle is 7 years old or wait until I reach 60,000 miles?