An oil seep near the ruptured BP wellhead in the Gulf of Mexico is casting new uncertainty over BP’s temporary success in plugging the leak. Oil stopped flowing from the well on Thursday after BP successfully installed a containment cap. But US officials say oil and gas has begun seeping from the sea floor, leading to fears of another hole in the well that could make the spill even worse. BP wants to keep the cap in place and has been granted additional time to conduct testing.