The cleaning tools removed wax buildup, enough to fill 11 55-gallon drums, but failed to find the missing part.
The pipeline operator, Alyeska Pipeline Service Co, downplayed the risk of the missing ring, saying there is a low probability that the ring would interfere with a check valve that stops the flow of oil in case of a leak.
A company spokesman, Mike Heatwole, said "We’ll just keep looking".
