A leak like that is never a good thing. It'll be too slow a leak to make a lot of difference when running but it could be rapid enough to make starting a little more difficult. Let the gaskets work with the oil for a day or three but then I'd suggest trying to tighten the rear cover in case it's come loose. Don't try to tighten super hard but a firm twist of around 6 foot-lbs would not be out of place. If you're not sure about torque amounts 6 foot-lbs would not be enough to open a new small jar of pickles or jam. We're talking very fine aluminium on aluminium threads so you don't really want to go with much more than that.