Interesting to read how well the hot air treatment works. I have tried to brighten up faded Flymo decks with all the usual cutting compounds and polishes but other than putting a shine on the faded plastic, no improvement. If it comes to a repaint you will need to roughen it up with 400 wet or dry and then apply a plastic specific primer as used by car bumper repairers and probably available at Halfrauds.
Al-ko, beside being a major manufacturer of caravan, motorhome and trailer chassis, make some decent garden machinery.
Way back in the 80s they made a grass collecting ride on where the deck exited to a rectangular tube with a conveyor belt inside it carrying the grass to a big upright bin at the rear.