There's an issue on the ST220 because Ford fitted a larger, heavier rear bumper but didn't include any extra support. What people have found over time is that the bumper "sags", and a gap appears below the rear lights. Whilst it's usually just unsightly, some people have actually had their bumpers fall off because of this, and at £600 for a new one, sense of humour failure usually takes place.
Ford issued some foam blocks to hold the bumper, but they're over £100, and not always effective. What is effective though, is the fix that the owner community came up with, which takes 10 minutes and is just drilling 5 holes and fitting 5 screws. The posts below should make it clearer!
http://www.stdrivers.co.uk/forum/to...rear-bumper-thread/page__st__1200#entry202717
http://www.stdrivers.co.uk/forum/topic/19528-rear-bumper-pics-screws/