YIKES!!!!. I cannot think of any bearing in the engine that is a ball bearing. Unless one of the oil pump bearings is like that. Can you tell from the cage how big in diameter the bearing might be? Possible front or rear crank bearing but I do not know their construction. It is not good though to find that in the oil screen. I would be parking it untill problem is diagnosed.

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Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel