Ok what you said Blknight made perfect sense when I read it again this morning.  Must have been more tired than I thought 
As for the cause of the leak though it was definately the splines.  As when I went to undo the big nut this morning, I put the brake drum back on and pulled on the handbrake.  Then I put the breaker bar on the nut and gave it a big shove.  Only to find the nut was finger tight 

  So after cleaning everything up I put the unit back together as I found it but did the nut up tight.  I figure it was only leaking because the nut was loose.
I'll find out after a week of driving if that was a smart thing to do or not.
I found it interesting though that the brake drum had only one locating screw and only one hole however the output flange had two threaded holes as per the Defender pics on the thread that was mentioned earlier.
Thanks for the tips.
 
			
		
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