Mike Busch writes an excellent column in the EAA magazine and talks about engine problems and their diagnosis. Give him a try. Could it be fretting of one crankcase half against another? That would be aluminum on aluminum, but should also produce some oil oozing.
Are aluminum pistons scuffing on cylinder walls? If walls are cerma-nil or some other ceramic impregnated coating of the type the ECI uses in their cylinders, the wear of the walls may be slight compared to erosion of aluminum pistons.
But I concur, trend up and increasing metal flakes are not a good sign.
Please let us know what you find.
Fred Moreno