I re seal all my film cameras using self adhesive foam that I buy from a craft shop, over here it's sold as 'Fabfoam' and comes in A4 sheets 1.5mm thick. I also buy sticky back black felt in the same size sheets for doing the ends of the film doors.
The trick is to use a rotary cutter, another craft shop item that once you have it you wonder why you ever used scissors, not a scalpel or a craft knife - they drag the foam no matter how sharp they are. The rotary cutter just cuts, right down to 1mm wide, I cut it thinner than it is thick. Use a good steel rule and one of those plastic cutting mats, it's just so much easier.
Clean the old crap out with cocktail sticks and lighter fuel. I then scrub the channel with my wife's toothbrush. She hasn't noticed the taste of Zippo fuel yet.
Peel the backing off the thin strips as you feed it into the channel, and push it into place with a cocktail stick. Cut to length once it's in place, cut the felts for each end, and the job's done. If you think you can't get the felts in the right position easily, lick the sticky side then position the felt. The moisture will allow it to slide a bit, then it slowly evaporates and sticks fully.
I've done about 10 or 12 cameras like this now, every one is light tight and free of horrible sticky crap, and I have enough foam and felt left for as many again