Got oil seeping past main nut in centre
flange, should there be a seal there or something ?

Hi Kevin.
Theres no seal in the centre of the flange , dont be tempted to tighten the nut though, as there is a crushable spacer that sets the preload.If you tighten more than the preset amount the spacer will be crushed and the bearing preload overdone, the spacer then has to be replaced.
It may be the pinion seal however , to replace this you need to mark the flange and nut , unscrew counting the number of turns, replace the seal and tighten the nut to exact original position.
Try a few searches on pinion seal replacement.
Paul

MMmm strange one but not impossible. It's not possible there's too much oil in there? is it?
You might have to remove the nut and use a sealant on the threads. Studlock or threadlocker would do.
As already mentiond don't overtighten the nut or you'll upset all the diff backlash settings.

Have removed nut to have a look, how do i put it back wright ?.

had took it of before i knew
not to, now in poo!