Simple Green is great for doing this. It really lifts up grease & most of it will just wash off without any rubbing. I say wash off, but I don't use a hose to do this - I just fill a spray bottle with water & spray the Simple Green & grime off the engine. This is a pretty easy way to do a basic clean to see if that area is still leaking oil.First, you have to find the leak.
Where is it coming from? If you can't pinpoint it with a flashlight, degrease the general area around where the leak is coming from