I personally won't run a car without Duralube - even my 560 sel is treated with it. Slick 50 I have heard also works but does something to the metal so that when you want to hone a cylinder at a later date - it makes it very hard as the honing stones have trouble cutting the metal due to the Slick 50 deposits. I started using duralube 10 years ago. I tried it in my lawnmower (not an IC engine - just aluminum bore) and that lawnmower as edged my 5 acres and trimmed around the trees and shrubs for 10 years and I have never touched the engine and it still does not burn oil and has good compression.
My daughter ran her Duralube treated VW Diesel dry because the valve cover gasket was leaking and she never checked the oil for 6 months. A lifter started knocking and it sounded like a pounded out main bearing. Only 1/2 quart of oil drained out of the oil pan. I tore the engine apart and there was no scoring or marking on the shells. The pistons rings had only a slight razor edge to them. I changed the lifter and reassembled the engine. That was 2 years ago. The engine uses 1 litre of oil every 3000 miles and still runs great. My 1980 Olds 350 4 barrel has been treated with Duralube and even at 30 below not plugged in - it cranks rapidly and fires. A friend of mine has a 5 hp air compressor that would dim the lights when it started up for 30 seconds (low supply voltage). We changed the oil to pure Duralube and the lights only flicker for a second or two when the compressor starts. That was 4 years ago - and it still runs great. He now uses Duralube in his 1967 Chevy that he restored. Last year my son got a "new" Jetta diesel that needed an engine rebuild. We rebuilt it and after it broke in - treated it with Duralube. The car uses 1/2 quart of oil every 4,000 miles. Do not use duralube on an engine that has not been broken in as it will never break in properly due to the reduced friction that will prevent the rings from seating.
Some out there still think it is snake oil. As you can tell - I swear by it. Cheapest insurance against engine damage I have found.