Hmmmm, strange that the old one did it also. I'm wondering if ?maybe? you could be torquing the drain plug down too much. When you try the black fiber, just tighten it good and snug but not enough to cause the washer to start twisting. (I use a short/stubby box end wrench) Just remember that the washer is "only" the "seal" between, what is supposed to be, two flat, smooth and parallel surfaces.

meller