This sounds silly.
"WHAT ABOUT OIL LEAKING FROM CRANKCASE" is this a question?
Answer?: The engine contains oil and when seals and gaskets get old/hard the oil leaks past them.
The crankcase is seals with gaskets and seal. The source of the leak is to be found and the gasket/seal is to be replaced.
If unusual cases where you have a crack in the engine block or head or metallic component, that component is to be replaced.