During the chunin exams, when Orochimaru attacked Konoha, the Third Hokage managed to seal the hands of Orochimaru, rendering him incapable of using any jutsus.
But later in the series we see that Orochimaru did use jutsus. For eg, during the battle with Naruto he uses the Kawarimi no Jutsu.
Though it has not been depicted that he uses hand seals to perform Kawarimi no Jutsu, but I presume that a jutsu of that level needs a hand seal to be pulled off. So, Orochimaru had never lost his jutsus.
Next, Sasuke managed to absorb Orochimaru into his body which was sealed off by Itachi using the sealing powers of Sword of Totsuka. How then is it possible for Orochimaru to be present in someone else's body and "pop out at will".
So how is it that no sealing techniques work upon Orochimaru?