You have the same filter cutter that I do! When I cut my filters open, I disassemble the element by tearing off the end caps, one pleat at a time. Just looking at the outside of the pleats doesn't show what the filter has caught. You need to look at the bases of the pleats. After I have the element cut loose from the end caps, I spray the element, which is about 10 feet long, with a can of brake cleaner and catch everything that comes off in a clean pan. Then I wait for the brake clean to evaporate, and inspect the debris.