Question Author
Thanks to both of you. It's just that the fridge door sometimes comes open, so it's not sticking very well.
The DIY kit doesn't sound very convincing. One of the reviewers said they had to use tape to keep their fridge door shut because the DIY kit seal wasn't the right thickness! And it says you attach it with glue, whereas original seals just use screws and clip in, I think. But thanks for the suggestion.
I also just read that using nail varnish remover to clean the seal might help.