Ok I know most of you saw the title and went WTF but i saw this when i was reading that naruto also has a shishou seal as well as the Hakke seal and the shiki fuujin. the frog mentions the Shishou seal here
and it seems this seal directly effects how much of the kyuubi chakra is released from naruto's body and if this seal is broken naruto will become the kyuubi if he can't control the chakra. and the seal will break eventually because this is the seal that gets progressively weaker with time not the hakke seal or the shiki fuujin.
since the shiki fuujin holds the kyuubi and the hakke seal seperates the chakra the sole function of the shishou is to keep the chakra contained. so its not the shiki fuujin weakening because if that was the case the kyuubi would simply escape naruto's body instead of naruto turning into the kyuubi which is why the shishou seal is needed but due to it not being a lasting seal it will either break with time or be reinforced by the seal frog. but i'd guess it wasn't made to last because minato eventually minato would want naruto to use the kyuubi chakra to use some kind of jutsu as mentioned by jiraiya.