[PsYcHe]

The carpet splits just under the seats, and it's 4 torx bolts to undo the seats.. Depends on where the plug is for the heater as to how much of a pain the'd be to replace. I'm guessing they're in the floor vents just under the seat.

EDIT: Just looked on ELSAWin.. Looks quite easy to do, they're directly under the vent under the seat, so undo seat bolts, slide or lean seat forward (or back, depends what's easier for access), take cover off, remove unit and the plug is just underneath.

Part numbers: 4E0 819 013A for left, and 014A for right. Around 130 Euro each according to my out of date ETKA.