I just tried skimming through that video, sadly youtubes translate korean to English isnt the best so i couldnt really follow too well. but from what it looked like, it was not the coating coming off. coatings are 1-10 microns thick (.001-.01mm) and what i think he was calling a coating removal appeared to be just oil or some other residue that got gummy from another ring that got onto the element. Oil moves around lenses in weird ways. No iris is ever lubricated, but somehow grease finds its way onto the leaves. Having received training from Zeiss and Canon repair facilities here in the states, Alcohol is what they use. you just have to be careful because it may not be good on other parts of the housing. Acetone is popular for the really hard to get grime that can build up, but that will dissolve plastics if you are sloppy.