Here it is. I’ve found it. The single most useful setting in Scrivener.
This is in the Compile window, and it allows you to globally find-and-replace things in the document prior to it being exported to whatever format you want to export it to.
The image above is what my settings for this window look like. It’s set to clean up all the bullshit little formatting errors (like quotes curling the wrong way after dashes) that drive the copyeditor crazy. Because I do a lot of writing in plaintext, it also catches the em-dashes and elipses I miss converting from their plaintext equivalents (I still have to convert smart quotes by hand, but that’s easy from the menu).
Hooray for automation!