How do I fix a Libreoffice document that is corrupted?

When I try to open the document, I get this message: Read-Error.
Format error discovered in the file in sub-document content.xml at 2,18067(row,col).
I’ve spent several hours on this document and hate to have to start over.

Take a copy of the ODT and open the copy using an archive manager (rename the file to a .zip extension if necessary). Extract the content.xml file. Open this file with a suitable XML editor. It will be likely that row 2 contains a very long line of XML. Scroll to character 18067. It is likely at this point there will be an obvious mistake in the XML. It may be minor or major. Once you fix it, simple reinsert the fixed version of content.xml into the ODT copy, again using an archive manager. Try and open the amended ODT using LO.