I made my own out of a 2lt plastic milk carton copying their design ,My front forks now need a full service but it has stopped the right hand seal misting for several months now
Yeah it's an old trick and really does work. Used to use old photo film too, but digital photography blew that one away, but any thin flexible film will work.
If the seals are well past it there may be no chance of it working, but when it's just dirt and rubbish causing oil to weep past this trick works fine. Always worth trying before paying for a new set.