The standard pinion has a bolt (well, at least it does on the Disco2).
https://www.aulro.com/afvb/images/im...015/06/560.jpg
It should also have that flange to keep the mud out. Not sure why it wouldn't or if its sensible to run it without one, especially at the rear.
https://www.aulro.com/afvb/images/im...015/06/561.jpg

