wheres my leak

If you can't visibly see where it's leaking from pressure test the cooling system. You'll see it then bug time. You should also check your oil, make sure nothing is leaking into the crankcase. As far as seals for the water jacket go, you have the water pump gasket, intake and head gaskets, thermostat housing gasket, and all the freeze plugs. You also have to consider a crack in the block or head, hopefully it's nothing that drastic. A leak could be further away than where the rust spot is, coolant can run along something or if it's under pressure can spray a good ways. Check the coolant reservoir thoroughly too, as well as radiator or reservoir cap and drip hose. Again pressure test can reveal leaks pretty quick.