Hi! Whilst I have not had that direct fault I have had the release cable for the seat break or at least the plastic ends break. I had to take the seat to bits to replace, but did notice in my 3 or 4th attempt to get it to latch that once the actuator starts to fail due to I think cable stretch you have to replace the whole lot. Not a difficult task as you remove the rear plastic seat back and the lower seat covers on the side where the switches are. Be careful how you remove this as it is easy to break a lug!!! If memory serves they are not straight pulls but slides!! hope this helps a little!!!
Always said I would go back to a 6 series