FWIW, my Disc 3 is the only one scuffed, and quite badly too. And no more copies at the store

Sounds like there may be no point in trying to replace anyway...
Edit: The disc 3 played perfectly after all. The doc is very good, certainly one of the best I've seen. Not having seen the theatrical cut, I have a much better idea of what was added in the director's cut now. Some of the stuff that was cut seems quite important to me, to getting you more involved in the story and to understand motives and circumstances etc.