The transcript of the part 6 contains the following text:
Oskar Gröning: "I see it as my task, now at my age, to face up to these things that I experienced and to oppose the Holocaust deniers who claim that Auschwitz never happened. And that's why I am here today. Because I want to tell those deniers: I have seen the gas chambers, I have seen the crematoria, I have seen the burning pits - and I want you to believe me that these atrocities happened. I was there."
I emphasized the critical part. Portuguese denier A S Marques wrote a letter to David Irving, in which he pointed out that the words "the gas chambers" were absent from Groening's speech in the documentary itself - both in the original German, and in the translation.
Upon checking, this claim turned out to be correct. Somebody has deliberately inserted the words "the gas chambers" into the transcript, and they've spread over the Web. This is the kind of thing that keeps deniers ticking.
Update: Mr. Rees has clarified the issue in the comments. Also see this posting. It's weird that the editor(s) chose to cut out these most important words.