I had rust all over inside and out of a gec radio knife I got yesterday not deep rust but it was spotted everywhere I have 3M polishing paper which I have used on several of my knives. To get it out of the inside I figured I’d use a popsicle stick with the paper wrapped around it, it was too thick to get in the very bottom towards the back springs but it provided a good amount of friction to really get the sides cleaned up well. After that I folded a small piece twice and put a toothpick down in the corner of the paper so it could get the back springs and reach everywhere down in there. I used pieces that were big enough to hold both the paper and the tooth or popsicle stick. The paper worked really well as it gets less abrasive as you use it so it ended up having the same kind of satin finish it does when new. I used the 30 micron paper. The coarsest from the pack I got from Amazon.