Anyway, they offered to send out a replacement cup as soon as I gave them my full address, with the understanding I would also ship my damaged cup back to them.
I'm pretty embarrassed to say that after telling my story to my SO, the "crack" FELL OFF the cup!! It looks like it was some random dented silicone left over from the mold or *something*, but I have no idea how it lasted there for 10 months without me noticing it, even through my sporadic boilings and scrubbings every month. So I wrote back and let them know that, and they replied almost immediately and still want me to send it back for a replacement so they can inspect it.
Anyway, I'm super impressed with their customer service and what a difference from when I had a genuine crack in my Divacup! It took them *months* to get a replacement out to me. I'm so sorry MC UK can't ship to the United States anymore because I certainly recommend them.