Singapore updates - experimental front wing and diffuser
McLaren tested new wing with totally new
end-plate in Singapore but did not use it in qualification or in race. (They tested this piece already in Valencia and at Spa I guess).
McLaren also used a new symmetrical rear
diffuser, replacing the previous asymmetrical design introduced at the Nurburgring.
They had also new floor. McLaren changed Hamilton's monocoque due to KERS cable problem. It was easier to change the monocoque than to repair it. So it was not because of performance reasons or new parts.
You can read more about aero updates here: http://www.f1news.cz/technika/33249-ino ... ni-kridla/