There are few certainties in life. Oh, of course there’s death and taxes- those are a given, but another immutable is that of the durability of the Mercedes OM616 diesel motor. While only producing a maximum of 72-bhp, the cast iron block oil-burner has proven to be one of the most long-lived of any consumer-available engines. That claim is lent credence by the presence of today’s streetwalker subject- which is a 1980 W123 240D. This 30-year old benz, while not showroom fresh, is amazingly clean with bumper snoods that appear to have survived the eroding effects of sun and smog. The interior shows few signs of wear, and even possesses the original Becker radio, which probably only plays 99 Luftballons. The most amazing aspect of this clean machine? Well, that would be the mileage as the appearance belies the distance the car has covered. If the odo is to be believed, this car has 302,798 miles under its brown belt.  Of course, for the OM616 that’s just getting started. It’s simply remarkable that the rest of the car has remained intact and so clean considering all the road time. It ‘s also a head scratcher that so slow a car would last this long, considering all the more-modern options available. The top-end on the 240D is about 88-mph, and acceleration can be measured by the same mechanism used for determining glacial recession. So, what’s the asking price for this slow but spectacular diesel? Well, the seller wants $2,500 for the 4-speed 4-cylinder Benz. That’s a price that puts this in the realm of possibilities for many, and as it’s still got about 800K left before the first major service, that might be a good, albeit slow investment. [nggallery id=44]