MY '87 560SEL had 350,499 miles on it the day the little girl in the Toyota totaled it. Original engine and to my knowledge, the heads had never been off. I believe it had valve seals and more than one timing chain done over the years. Car had fanatical maintenance over the years by its three owners. first two owners probably put some mechanics kid thru college. Me, I'm cheap and do my own work. Trick with that engine seems to be to keep up the maintenance (including 3k mile oil changes) and never let it overheat. They are not TOO expensive to work on.