I'm not sure exactly where you're referring to a small slot and hole. If you go look at http://www.acehobby.com/ace/PDF/Engine/PRO_Eng.pdf
You will find an exploded view of the engine. The view doesn't show the kind of detail you're talking about, but perhaps you could refer to its location in relation to the part numbers on the diagram. I've only taken one of these engines down in the past 4 years, and I don't remember the specifics behind the front bearing.

Brad