It says the rear sidelight is a 5/21W bulb! I asked the guy, surely you won't need a dual filament for a rear sidelight - he went yeah prob not, must just be the single filament bulb of the same fitment... wasn't. Not been back to return them but when changing it, it looked like a W5W bulb? better double check though.
Also to replace the bulb you need to pop off the rubber covers of the bootlid, take out those screws and one from behind the plastic cover that comes off and you remove the whole light unit.