Hi Wasa,
I have done three steel pan conversions to date, I have usually found like a grey paste around the magnets which I am assuming has some metallic substance to it. I have never found like shards of metal, only the grey paste ike substance.
What ever it is I am assuming it is better attached to a magnet than moving around a gearbox. I am changing out a filter on my steel pan next weekend, depending on what I find I'll post some pictures if there is anything noteworthy. The magnets, all four of them will be going back. I have always found magnets in the plastic pans I've taken off.

