Why is the seal changed after Kushina helped Naruto in controlling the Kyuubi? There was no sticker seal in the Kyuubi's cage and it turned into a circle lock with red cage.
It was like this before with a paper seal in the center
After meeting kushina it turns into this, with tomoe lock in the center and a red cage
After meeting Kushina and taking the Kyuubi's chakra, it's implied that Naruto now has a lot more control over the Kyuubi, and thus does not require the paper seal to assist in warding off its influence. Naruto took the seal off on his own during the fight to subjugate the Kyuubi, and thus, no longer exists.
Note that the paper seal was put there by Minato as a stop-gap to prevent either Naruto from voluntarily taking off the seal, and to keep the Kyuubi in check should its power or influence grow out of control (as evidenced by the Pain arc).
