Looked at my tools, and nothing looks amiss there, but I did have another thought on what this is - it looks like it could be a roller from a needle bearing. It looks chromed and hardened with some scoring on it. I still have no idea where it came from or how it ended up in the webbing in the engine block near the oil filter housing...

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2012 xDrive35d
2001 BMW X5 3.0i 5MT
and two 1987 Corvettes - Callaway Twin Turbo and Guldstrand Grand Sport 80
Block Tester