I have noticed this morning some milky water from the bottom of the rad also. when I drained it the coolant was clean though so its residue from the bottom but im still worried about how it got there.

im also worried if this liquid metal will hold as there will be water pressure directly behind it trying to blow it off, id like to fill from inside the block as then the pressure would push the sealant into the hole but its not really possible. im thinking I need to get the motor out, upside down so I can look in there easily and see how bad it is, looking from underneath around the hole looks very thin like tin !