I have seen no major problems with the newer 60x engines. If you maintain them, they will last forever. You will get a cracked head here or there, but it is my opinion this was due to owners neglect/error at some point. The 3.5's did have some problems, but alot DID last and are still on the road today. The rest of the 60x family of engines are terrific, IMO.

I've seen some high mileage 96 to 99 E300's, 100K to 190K and as far as I know the engines have never been apart. One '96 E300 I looked at with 100K miles was -very- neglected. It didn't look like the oil had EVER been changed, but it still ran perfectly.