[midlifec]

There's an easy way to do this.
Open the book in Sigil.
Identify what the ? stands for - it's usually an apostrophe, quotation marks, hyphen or row of dots.
Get to "find and replace"
Drag and drop or right click and copy the ? from the text to the find and replace box
Replace with the right punctuation mark
Voila! Repeat with all the parts of the book extracted by Sigil.
Piece of cake.
It's a problem when ? stands for two marks (eg) - and ... but the text is a lot more readable if you replace all of them with a hyphen.

PS Sometimes you have to have the ebook displayed in the "code view" for this to work; I don't know why