you got the wrong diagnosis dude....

if your oil is jet black becasue of diesel ash and no water in the
oil then forget about the engine....

here is your problem...

1. the neck of the radiators is made of plastic.... it very easily cracks
and your has cracked on the under side and there is enough neck left that you are able to reattach the hose... but get out and watch it and you will see coolant trickling down under the neck....

you need a new radiator.....the reason this happened is because its gotten really hot and perhaps you thermostat is stuck closed or is not opening fully..

So first thing is to remove your thermost....

second buy a used radiator.... or try some jb weld... jb weld worked for me for a couple of months... while i was looking for a radiator...

If your head gasket is bad you might see water in your oil.... and if your head is bad you would be smoking... cause the valves would be letting oil into the cylinders.