horrible white residue

I keep on finding books that have been poorly repaired using a sort of buckram tape. They were mended about ten years or more ago. I am trying to repair them correctly but have not had much success in getting rid of that horrible white residue. I have tried methyl cellulose and it works somewhat better than most things but I still have to rely on scratching it off with a knife--and that is not 100% successful. Any suggestions?

I take it the white residue is the old gum from the tape. Can you try lifting it off with a piece of new tape? That has worked pretty good for me to get rid of old adhesive on books.