For those who are thinking about doing it, it’s doable. There are alot of instructions and information out in the web. It does take time however, so make sure you have an afternoon free (in my case 3 afternoons). I experimented with non foam light seals, ie, a rubber type but was not successful as it was so damn hard to cut and fit. I suggest using black felt or buy a kit online from Jon Goodman. Here are some useful links which has helped me alot. Without these guys it would have been close to impossible. Thanks!
More specific for Canonets QL17 Replacements:
Solvent is useful to make the cleaning of the old light seals easier, and a movie on the background helps kill time.
For those who have done it. I feel like I am part of the club! lol. My patients can be seen below.