HELP! Oil in cooling liquid

I have a Audi s4, 94 mod. It has a 4,2 L ABH engine.
I get oil in my cooling liquid. I have disconnected the gearbox oil cooler that integrates with the radiator. It didn`t got any better after this. So I changed cylinder head gaskets. I also checked the flatness on the cylinder head, but they where totaly flat.
I didn`t see any faults on the gasket either.
I need som advise from eksperts. I still get oil in my cooling liquid. I have replaced the cooling liquid several times.
I hope someone can help me. I have a suspition there is a crack in the cylinder head. But since they where so flat is seems strange.