Mory,
I think in most situations it's a mistake to try to force someone to do something in any kind of a relationship or transaction. I understand the seller has a legal obligation to complete the transaction, but I'm also a practical person. I don't "avoid" crusades, but I pick the ones that have a good chance of winning, and are worth the winning. If it's something minor, or easy to get somewhere else, I'll walk away. I'd rather do something enjoyable then spend my, and some ebay employee's, time beating up on some recalcitrant seller (something I wished I learned earlier in my ebay experience).
There are times when something small should be contested because if not it will establish a precedent that will encourage others in this kind of behavior. But since no other seller will know the outcome of this, and since you'll probably never buy from this seller ... well, it's your call.
P.S. This has come up before on this forum, and it seems like they all turn out for the best. Usually the seller had some emergency.