They are moulded. The shouldn't be stuck with any glue, what happens when you need to remove the bumper to fit new bulbs??!
Anyway, with my old 197 I simply heated up the two cut out loops on the bumper with a heat gun, the hoop bits that clip round the clips on the wings get mishapen inwards. (anyone have a pic of the bumper clips so I can explain might be handy?!)
So they just need re adjusting/pulling out with some heat, let them cool down, refit bobs yer uncle. I never had any issues after this.