The third and final launch attempt of a homegrown space rocket has been postponed until next month.
The Ministry of Education, Science and Technology on Sunday said the seals in the coupling device were the source of a leak prompting Friday's launch to be canceled.
The seals will undergo precision tests in Russia, where they were made.
Korean and Russian officials will establish the cause of the defect by Friday and fix the problem. Seoul will then set a new launch date no later than Nov. 15.
Technicians discovered the gas leak in the coupling device connecting the first stage of the rocket just five hours before launch on Friday while injecting helium into the booster. One of the rubber seals was damaged. Helium is used as an internal brake in the first-stage booster rocket.
The science ministry is holding a meeting on Monday to discuss the problem. Officials are expected to argue that it is impossible to meet the prior launch deadline of Oct. 31.
Korea needs to inform the International Civil Aviation Organization and the International Maritime Organization of a launch at least a week in advance of the launch, which takes three days to prepare. That makes it likely that the next launch will happen between Nov. 10 and 15.