The crankcase isn't sealed for the reasons listed above, but the filter side of the lube circuit is indeed; especially since all of us regularly change the two little "o" rings on the filter stem
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Pop the top of the oil filter up/off and your drain time will be much less. Those two little "o" rings have as one of their purposes in life to prevent oil from draining down from the filter side of the lube "circuit" when the car sits.