Yeh I've seen that, must have been option before 03 because I've seen older ones with isofix. Looks like a seat change would be the only way then.
How much are you wanting to spend?
are you going pre face lift or face lift?
I wouldnt be worring about seats at the moment , i would be more concerned about finding a decent solid disco. As to the oil around the transfer box , i would say 90% of the ones you will look at will leak ... Its just the fact of from where. Apart from seals leaking behind propshaft flanges , which are cheap and a easy fix, they leak from intermediate shaft , which runs through the transfer box .