Unlike schudel5 I have a lot of pinball repair books.
None of which are very helpful. I can't remember when I last opened one of those books up.
Because pinball spans many generations of technologies and approaches, the game manuals had to provide most of the information needed to repair pinballs.
Want to fix a Corvette pinball that the LT5 motor isn't shaking right? You are going to NEED the manual. And the Addenum to the manual. A lot of pinball repair is very specific to the machine you are looking at.
Each machine produced had different mechanical toys/assemblies and frequently different boards.
So, the best 'books' for your personal collection of pinballs is to have all the manuals for the machines in your collection.
The pinwiki is a strong resource for me now.
Because I needed a book on how to 'bulletproof' Bally/Stern games from the 80's, I just printed out 36 pages from the pinwiki. That is my 'book'.