[chiphead]

I can't imagine what could be making that much metal and not leave telltale signs in the engine. If it's NOT being poured down the intake, it's gotta be coming from a wear surface inside the engine. I would expect that the source would show gouges and areas where metal is missing. Piston/ring wear should show scuffed pistons, scuffed cylinders and rings with big end-gaps. Big wear surfaces should be painfully apparent.

If no source is found, then check the exhaust. Could be a bird nest, rust or a bunch of crap in the headers, exhaust pipes or mufflers.