Well I would think the problem lies with the heat treatment of the steel lifters that grade of steel would need to be case hardened ,the camshafts are made of cast iron and these are now made with mechanical chills in the molds so that when the molten iron is poured the halides rise to the surface and so after machining the camshaft does not need to be hardened,I cannot believe the V8 AMG engine is put together by people who do not know how to assemble it properly so case hardening may well be the problem,I wonder if the guy can ask to see the parts that have been removed from his engine,and maybe take some photo's,then we might have some idea what the hell is happening.