Update to my seat belt guide sanding: Well pulling it in conjunction with the passenger side I could feel little difference. It seemed to feel smoother but it still doesn't pull back up into place with any significant improvement and lay flopping down the side of the seat to invariably get trapped in the door. Don't think about changing the seat belt guide on the seat itself as that will make no difference as I was testing mine while they were not in the oem guide. The answer must be in the mechanism itself. Its probably designed to have a longer travel so more belt is out of the mechanism and then it puts more tension on the return spring. If that is how it works. Other car seat belts seem to have tension on them still in their resting position. For the Copen its just flopping about and only really goes in further when you assist it. A bit like a tape measure. You pull it out far and it snaps in to place because you have a lot of tension on the spring and gives the tape momentum. If you pull it out a short way it won't also slide fully back in. Just a thought.
Silicone Spray I sprayed both sides of both belts with silicone and took out the washer mentioned in the guide. It works perfectly now.
I did the same, without taking the washer out even, and after a few days suddenly the seat belts "just work". I've also noticed that if I recline my seats slightly, the seatbelt tension is less effective. It's like the belt direction of travel has to magically align with the guides on the side and the seats and then suddenly it all works.
Another excellent post. I sanded the guides and sprayed with silicone. I also gave the belt a clean and ironed the belts (tip from a BMW convertible owner who had the similar issues). Currently they glide back much easier and don't flop around on the seats. I find they twist in the shoulder guides and stick, so tend not to use them at the moment.
Thanks everyone (and thanks Copenworld for storing useful stuff like his for years until someone like me needs it). I got an Advisory on my last MoT and don't want to risk a fail so thought I should fix the seatbelt retraction now. The hardest bit is having the courage to yank the trim hard enough to release the four clips: fear not, you won't break anything. No spanner, no wet & dry. The guide had a lot of dirt & grease on it so I fed a strip of cloth through it & cleaned it with meths. That and a good old wash of the belt in detergent and it's fine. Not perfect but fine - I'm too busy grinning at my car to have any more time to fiddle with it.
