One of them was the passenger side rear seat folding action, that allows access to the 3rd row.
While I have yet to use the 3rd row, I would have to use that side as I have a child seat in the other side which isn't very movable once secured in.
So having a quiet afternoon at work I popped out to the car park to see what the problem actually was and if i could fix it.
Turns out it was a surprisingly easy fix!
Simply lift the seat base to get access and you'll see when the seat back is folded down, there are 2 catches that are activated by tensile cable pulleys. Over time the cable had become stretched so would no longer pull enough to activate the pulleys:

Circled above
Thankfully Nissan seems to have thought this through and on each side there is an adjusting ring (you can see the slack in the cable):

Just pull it free from the housing (which can be a little tight on the one next to the seat belt retainer, but the plastic just moves out of your way without any damage) and UNDO the adjuster.
This makes the cable housing CLOSER to the pulley, reducing the distance the cable needs to move to activate the latch.

It can take a little fine tuning to avoid the latch activating inadvertently when the seat is upright, but I found half turns then check worked for me!
Hope this helps!