Good catch on that video.
The presenter seems to be Łukasz Mrozik. I can't find his title so I take your word for it that he is head of archives. At 25:22 he enters the B41 gas chamber (IV) where he says:
Look at this one right here. What makes it quite unusual in comparison with the previous ones are the bluish stains that you can spot on walls, on the ceiling, pretty much all around the area. Those blue stains prove that Zyklon-B was used in here. Zyklon-B, which is probably the most famous poison used in the Holocaust because it was the primary [type] of poison used in the gas chambers of Auschwitz-Birkenau. For years, it was generally considered that it was a gas chamber but over time and more detailed research proved that it wasn't a gas chamber but a disinfection chamber instead. So this is where Zyklon-B was used ironically for its official purpose for disinfection for the disinfection of prisoner clothes, SS uniforms, [?] blankets, sheets, etcetera.
Contrary to his characterization, there is nothing ironic about using a pesticide as a pesticide. He then shows off the Zyklon can display. The added interior wall on the right appears to be gone. At 27:19 he reaches the B1 (I) gas chamber, where he says:
And over here you can see probably the most important object preserved from the museum grounds: the building bunker with the gas chambers. Three of them were built here at Majdanek and they are all here within the same bunker. This is the first one. At any site you will not spot any blue stains left by Zyklon-B because not Zyklon-B but carbon monoxide was used instead. These were pressurized exhaust fumes from some tank or lorry engines that were pumped inside through a special system of pipes that you can see very close to the floor.
I'm a bit confused here. Did the Germans collect engine exhaust and put it into pressurized CO canisters? At 28:37 he is at room 14:
The original carbon monoxide containers were taken away by the Soviets in 1944. They were shipped away to Moscow. So this is just an imitation of what they actually looked like.
At 28:48 he reaches "the second gas chamber" (chamber A/III):
... and here you clearly can see the blue stains left by Zyklon-B, this residue that proves it was used here. So unquestionably Zyklon-B was used in this gas chamber.
At 29:26 he says chamber B2 (II) could not have been used:
In the third gas chamber there are no traces of Zyklon-B and no equipment necessary for the use of the carbon monoxide. So we claimed in our research that although three were used only these two were actually used.
At 37:50 he explains that the shoes on display belonged to the victims "not only of Majdanek" but also "to the victims of Operation Reinhardt". He explains that Operation Reinhardt was headquartered in Lublin, which is news to me. Since Majdanek is also listed as a Reinhardt camp on the Hoefle Telegram, it would make sense for historians to include it under that designation, but they don't.
At 01:08:44 he answers a common question:
You may also wonder in the meantime why this crematorium was built so far away from the gas chamber. Well, it was constructed at the time when the gas chambers were no longer operational. Usually they were built right next to each other because it was practical, for convenience. At Birkenau for example it was within one and the same building. Here [?] it was a bit different as you already know. And this crematorium became operational in late 1943 so at the time when the gas chambers were no longer used for the extermination of prisoners.
Of course the old crematorium was also not built next to the gas chambers. But even if this reasoning made sense, he goes on to say that Jews were still being exterminated in late 1943. At 01:11:13 he's standing at the ditches behind the crematorium when he says:
Within less than 24 hours, it began in the morning, ended in the afternoon, on the third of November 1943, the German SS police security police functionaries murdered over 18,000 of Jewish women, children, and men right here on this spot.
If they could do that, what did they need the gas chambers for anyway?
Overall I think it's quite satisfying to see the museum tour vindicate revisionists. They are down to just two gas chambers, and they're unequivocal about Iron Blue stains, even confirming that the lack of blue stains in one room is evidence against Zyklon-B having been used there. Rudolf should be especially pleased.