I thought that putting a magnetic sump plug in the sump and in the trans pan would be a great idea, before reality hit.
Magnets only attract ferrous metals, in particular low grade steel (not stainless) and iron.
What iron parts wear in an auto, and to a lesser extent, an engine? Most parts in an auto are alloy, stainless or kevlar, and bearings in engines are not magnetic either. your crank doesn't wear, nor your block, in any big way.
Sort of a non event really. I guess if you DO find metal on the magnet, your in the poop.