Thanks for replying, I'll take some pictures tomorrow and direct message you rather than spamming this thread with them! My car is a 2003 with standard red leather, electric, but NOT heated seats.
The new seats with the missing yellow block I plan to install, are also from a pre facelift car (or so I've been told!). These are also standard red leather seats but are both electric and heated (and in better shape than my own seats). The passenger is good on mine but the drivers is tired, with the foam padding past it's best underneath on the outer (door side) of the seat.