There are several places that a self-propelled lawn mower can leak oil form. The most common of those places is from the carburetor. Yes, the carburetor. When you overfill the engine oil, it will be sucked into the crankcase breather and then into the breather tube and into the carburetor. Then that oil will drip out of the carburetor and it can also get ingested into the engine and burned up. This will also cause the engine exhaust to burn a light blue color.
Another place is the rocker arm cover. The seal can become split or the bolts holding the cover on can loosen and cause the cover to leak. First, check the bolts to see if they are tight and if they are, check the integrity of the seal.
Oil can also leak at the crankshaft seals. There is a seal at the bottom of the engine and the top is sealed by a tight fit between the crankshaft and the crankcase.
The last place is at the crankcase itself. An item such as the governor arm protruding through the case or the crankcase gasket itself will leak.
Now that you know where the majority of leaks occur from on a self-propelled lawn mower engine, you can find a small engine repair shop near you on our Locations page.