I contacted the seller, Joseph Victor, through his web page, because the page said that he would attempt repairs. I got back an articulate and friendly note complete with expectations regarding timing and possible pricing. So then I sent the mug out to Joe in New Mexico for a lookover. His response was that it was a warranty issue, and that he would be fixing it and shipping it back at his cost.
I got the mug back yesterday. And it looks new! It's clean, polished, re-sealed, repaired, and did I mention clean? Along with repairing and re-sealing the wood, Joe scrubbed all of the tea stains out. So I got a like-new mug for the cost of one-way shipping.
A+, 5/5 stars, would use again.