Sounds like he is being about as reasonable as one could expect. I wouldn't push it, you don't want him to stop being so reasonable.
For them to take the tank back and rebuild it will cost shipping, some tubes of silicone, and some man hours. I can see how they could make that work. On the other hand, to refund half the $ would probably put them at a loss just on material. If I were him, I'd stop being reasonable at that point.
It's not hard to find a bunch of helpers here to move a tank. IIRC the going rate is a 12 pack of beer per person to take home, and a few pizzas on hand. If I were you I would have them take the tank back to re-do it and eventually have the tank you want. There is no room for being impatient with something like this. Sorry, but it's the truth.