Thanks for your comments stevebfl. I managed to get the nut off and removed the flange to replace the seal. What I did was make a brace out of a piece of steel rod and the nut came off easy with the flange braced agains the garage floor via the rod.
What I noticed was no washer or spacer looking at me so I was going to ask - sould there be one? I think you've now answered that by saying hte crush washer/spacer is behind that bearinfg that I can see.
So, my next question. I chewed up the nut trying to loosen it with a chisel - butchery I know but we live & learn. So, I was intending to get a new nut. Either way I've lost the original marking on the nut. In that case I'm simply going to torque it up to the 180Nm spec. Now reading your post again its not clear to me whether you meant to say the 180Nm i way more than that required to originally crush the washer or, as you posted, less.
I'd be interested to hear your comments but I can't see any other option for me than to go to 180Nm.