I've seen the show on DVD, and many of the explicit moments have been cut. Some not so much, others yes. I haven't seen or at least remembered every episode's full original version, but I do remember that this show had explicit moments that were controversial that have been cut from the airwaves.
I disagree. I do not think it is a good idea to splice parts of Seinfeld, out of Seinfeld, for syndication. Personally, it seems to me that the show has never been off the air since it started and it ended many years ago. Would it's current status not already be syndicated?