Just a small addition, fitted an OE GTi back box earlier today (thanks to JackG for supplying). Had a bit of a problem in that the adaptor pipe I ordered was 64mm to 54mm, but the OE pipe work bulged very slightly at the fixing point to 55mm, so I had to bodge it a bit until a new connector arrives next week.
Tbh it doesn't look that different to the trims I had fitted previously, but I am much happier having the real thing on there.
Apologies for the state of the car, it will be receiving a serious clean later today.