An engine lubricant formulated as a complete crankcase motor oil or additive concentrate composed of a combination of chemical constituents including a base oil selected from a synthetic oil, a mineral oil or semi-synthetic base oil (hydrogenated oil) or combination thereof, an oil soluble molybdenum additive, a dispersant inhibitor containing zinc dithiophosphate, and viscosity index improvers and one or more seal swelling agents to lubricate the engine and recondition the seals of new and/or high mileage engines. Addition of a polyalphaolefin and/or one or more esters such as a diester or polyolester may also be utilized therein. The lubricant may be formulated as a complete engine oil crankcase lubricant, or concentrated into an additive for addition to conventional mineral oil based engine oil, synthetic engine oils, or blends thereof in an effective amount of up to 30 percent volume percent, typically from 20 to 25 percent by volume.