Here's how I fixed mine for about 5 pence:
https://www.volvoforums.org.uk/showthread.php?t=269885
It lasted fine, but I subsequently noticed a lot of play at the swirl-flap shaft, and ended up replacing the whole assembly...my write-up on that is below:
https://www.volvoforums.org.uk/showthread.php?t=275783
I'm not suggesting you have a go at replacing the whole thing, but some of the photos are useful to see how it all fits together.