I have some QC2s. The pads went to black dandruff quite soon on mine too. I got them replaced for ¥7,000!! Yes, that's <$60!
I was less than impressed when the same thing happened again after 3(?) yrs - however long/short it was, it was less than impressive. I refuse to pay again.
So . . . Remove the pads - you can see how on YouTube - then find a small, stiff nylon brush and remove the plasticky coating that pretends to be leathe from the still perfectly serviceable (most likely) cloth. There is a seam on the inside of the curve, but you can hold that together and brush. Just brush. Quite vigorously, but still carefully. The manly plasty will rub away. At the outside edge, you can use your thumbnail to scratch the grot away. The cloth seems to be glued or heat sealed to the rubbery ring and it seems to stay that way, which is good. It took me an hour or so to do both.
If the cloth rips, I'll rebuild with either leather (a little tricky as it needs to follow a double curve over the foam and round the ring) or non-rubb(er)ishy cloth using a contact adhesive in small quantities and clothes pegs to hold it till dry.
The headphones are great, but why they used this to finish them I fail to understand. Or do I: is it just a cynical ploy to get even more money from their customers?
To quote 'Private Eye', "I think we should be told".