Attempting to view (gnus-article-press-button) the diff patch, I got the
following backtrace.  Is this solved by fixing the parens as per this
Changelog entry?

1999-07-08 08:41:10  Lars Magne Ingebrigtsen  <larsi@gnus.org>

	* mailcap.el (mailcap-mime-extensions): Changed patch to
	text/x-patch. 

	* mm-decode.el (mm-display-external): Wrong placement of paren.