Is the question limited to the original engine? If so, my 1985 300D is a non-contender since the original engine failed at 330K. Now at 345K w/ replacement engine. No idea on my 1984 300D. The odometer showed 130K when I bought it, but when I pulled the cluster I found green paint pin writing like PickNPull uses.

I recall newspaper stories about a 70's Toyota Starlet or such reaching >1,000,000 miles on the original engine, but hard to believe it didn't have at least a valve job. In most cars, the engine isn't everything. A rebuilt Chevy small block is cheap. In our cars, a rebuilt engine is >$8K so it is kind of is everything.