307,000 on a 1997 Ford Escort wagon. Original bottom end, new head this year. Factory crosshatch hone pattern still visible in the cylinders when the old head was removed after losing a valve seat insert (an Escort CVT engine weak spot).
Been using Red Line for over 200,000 miles. Been using a K&N air filter for even longer, first as a drop-in replacement for the original, then as a cone filter with an aftermarket intake system that has now been on the car for well over 100,000 miles.
The car has a 5-speed stick and the original transaxle, though the clutch has been replaced a couple of times along the way. The transaxle has Red Line C4 + Mr. Moly (MolySlip) ATF additive.
I still get 32-35 miles per US gallon on the highway if I drive sensibly. And I usually do, out of respect for machinery that Ford never intended to go this far.
But I got over 350,000 miles out of a 1988 Festiva, so this is nothing new. In fairness, the Festiva was simply flat worn out after that many miles. Before that, it was nearly 250,000 miles from a 1978 Toyota Corolla 1200. That car became hard to find parts for, particularly at a reasonable price, and ultimately got retired when the distributor went. The distributor was an expensive little animal (several hundred dollars for the whole thing, as I recall, not counting installation). This kind of problem, the too-expensive part, is probably what retires most high-mileage cars that don't have a catastrophic engine or transmission failure and don't rust to dust.