after a bit of research I think the part number for GTI Mk5 FK Silverlines is FKXVW47. They have a different product code for the standard Mk5 golf dependent on weights of the car.
The Leon codes range from FKXSE74 up to 77.. their website is all in german and I'm not a very good linguist! but i'm not sure on the differences and whther or not the product codes are there to mark a difference in design or just manufacturer.. hence the VW and the SE