pm sent Golf,
Marlboro.. I don't know if you have tried fitting them but I just want to advise a few methods that might help you on your way. When you remove the current plates, inside you will find a bolt on the inside edge, you might have to remove this to get a tidy fit on the vents. I know that some models of Golf the horn touches the vent, so i suggest slackening the horn off and rotating out of the way!
When it comes to getting a good tight fit with the vent, it is best to jack the car up and climb under the bumper, when you push the vent in you will see it has 4 clips, its tight as hell so you might need to use a screwdriver just to apply enough pressure to make sure the vents mount up nice and securley
Hope this helps
Dicky