How to clean dust out of a Leica-type bottomloader

So I have a Zenit S (Zenith C) which is a direct modification of the Zorki 1 or Zorki S design to an SLR. I've put two rolls through it and I'm loving the lens and the feel.

Unfortunately my negatives get scratched to h*ll (hairlines all over and going in all directions) and I think there's a bunch of dust in the gate. The pressure plate looks fine aside from one big scratch that seems to be smoothed down.

How do I clean a Leica-style bottom-loader's film cavity and especially the gate? Can i spray canned air into it? Don't worry, I won't unless you convince me it's fine, since I don't feel like it would be good for the shutter.

Ko.Fe. said:

https://cams.retro-cams.com/2015/03/repairing-zenit-c-industar-50-2.html

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That's... drastic. Are there any special precautions before I remove the body sleeve?

So anyways, If you take the outer shell off this kind of camera (probably including Leicas and copies), remember to go very slow and make sure you don't lose the pressure plate, as pressing against the shutter crate is all that retains it and its two sheet-metal springs, which would be a pain to have to replace. Also remember that the screws are brass with cheap Soviet chrome sprayed on, as is the body--try not to scratch anything.

I did in fact fix the problem, which was a big old scratch in the metal of the film gate with a rough edge on it--no wonder it was scratching my film so much. I took two emory boards, one coarse and one fine, and sanded out the burrs--being sure to keep the shutter above the place where I was filing, so no grit or metal dust went in.

Now that's done... just to open it again and adjust the following curtain spring tension sometime-- 1/500th spreads out a little.

Eight screws and holding film table is "drastic"?

Ko.Fe. said:

Eight screws and holding film table is "drastic"?

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It looked scary at first glance until I understood that none of the mechanism was going with the metal sleeve.