I take the pleats and wash them in a varsol bath in a Ziplock container, then move a neodium magnet from an ID badge all though the varsol and across the interior surfaces for several minutes to draw any ferrous particles. This collects absolutely everything. When the magnet dries off I get a tiny bit of microscopic fuzz or just a small amount of ferrous mud stuck to the magnets. Lyc allows up to 9 pieces of significant size metal particles. I then agitate the varsol and dump it into into a black plastic shallow tray, let it settle, then drain off the varsol leaving behind varsol/oil residue and any non-ferrous metal, like panning for gold. Non ferrous particles are visible against the black plastic. I usually get some random tiny speckles of what look like aluminum, probably wrist pin plug wear. Pretty much the same result every time.
Next time use a vice. 1. To hold filter while you cut it open. 2. Take about a 1” section of the filter and squeeze oil out using vice. Use a rag/paper towel to catch oil and wipe off filter. Then open up the filter and you will see particles and metal much easier
