I've got a disco td5 seris 2, there is a problem with the plastic wheel arch trims; they have discoloured badly and gone rough, they used to be black now they are grey! have tried putting back to black on them someone suggested boot polish, but nothing works, has anyone else had this problem if so how did you rectify it please?...it appears no one sells after sales replacements except original from Landrover which I suspect will be very exspensive!!!!!!