Over oiling is better than under oiling. Any excess oil will just drip off the bottom of the filter and drain out the drain hole in the bottom of the dirty side of the filter box. If a little oil did get drawn through the filter, it would most likely fall to the bottom of the clean side of the filter box and drain out through the drain line on that side. When new there is a clear catch bulb and a plug in the clean side drain. You should keep that line plugged except to drain the bulb on the rare occasion that some oil or water does make it through the filter.