this may sound silly but your crank may have a groove worn in it from the previous seal.
This can be fixed with a speedy sleeve.
we did ####loads on the landrovers it was either #### steel or #### seals, first part number for land rover I ever learnt was a tranfer case oil seal ( how wrong is that)

if its re accured could be a number of things
,bloby on boost can do it it will blo your rear main seal .also check your crank shaft vetilation .It may not be the mechanics fault rear main seals are easy to do .

is your oil pressure in spec?

Hey there guys.
I have a concern. I have replaced the rear main seal in my CA18DET, and its now leaking again. I didnt take any short cuts, i bought geniune seals from nissan ( front, rear, and cam seals). I had it installed buy a mechanic, whom i am going to visit today about it. I'd like to know the predictable answer he will try and bluff me with, avoiding warrenty on his work. Any help would be appreciated. Clayton