So I ended up deciding to get a new Steel Battalion controller of eBay (my attempts to fix my existing one have made things worse and I think it's unsalvageable without more work than I'm willing to put in). I'm starting to get a bit of a fishy vibe off of the seller. First, about 5 minutes after the auction ended (I got outbid right at the end) I got a second chance offer, with the message "Looks like you won it after all". Then I just got an email from the seller claiming there was an error in shipping calculation; instead of the $18 quoted on the listing the label is for $30.
From eBay's perspective, if the seller miscalculates shipping and I've already paid, is it the seller's responsibility to eat the difference?