Just checked out the Etsy tetsubin. That guy's a crackpot. That pot is not worth the cleanup. There are always tetsubins coming up on Ebay; wait for yours.
As for me, I do collect antique tetsubin. Can't claim to restore them though. I'll clean the rust out, boil tea in them and use the tea to sop the outside of the pot, but that's about it. Of course the last tetsubin that I purchased I had a dickens of a time getting the motor oil out of it. Occasionally I'll boil water in it to try my luck at getting the smell out, but I would never drink from that pot. Right now it has a very faint motor oil smell to it. It also had a married, makeshift top to it. I threw it in the garbage and replaced it with a Japanese top that I purchased on Jauce.com (tetsubin lover's heaven!). Now it's as beautiful as ever!