So I got on the horn with Corbim today, and am happy enough with their response. They sent me this email, and I can live with this:
"Sorry that there was a defect on the leather upon receiving the package. We will warranty the leather for up to a years time no ?'s asked
So if you would like to finish the riding season with the seat, when the season is up we will pay for shipping via a fed ex call tag pick up
From there if you need any alterations to be done, we can perform those request while recovering the seat at no charge"
They also sent me an RMA for it, so it looks like all is well.