ok people i have no idea why there are 2 holes above the oil filter housing. the 1 has the oil filter sending unit in but what is the other hole above the sending unit for or is the sending unit suppose to be in the top hole? is the 2nd hole suppose to be open or is it suppose to be pluged and does anybody know what size plug goes in which ever hole is not used for the sending unit? thanks for any help on this. would this open hole have any affect on vaccum or how the car runs?