What does oil in the radiator mean?

I just got a Honda cbr 600 f2 and it had a crack in the radiator cap so I look in it and it had oil in it. I just bought the bike and it runs and rides fine but It has oil in the radiator. I called the guy and asked him and he said he thought it was cracked but he said a mechanic told him it was a seal that was bad. I drove it home and the dude drove it to meet me which was about an hour drive for him. And it rode fine. I'm just trying to figure out what I need to do to fix it.

Time to pull the engine and replace the head gasket, bring the head to the machine shop to get checked/decked.

Said earlier that it wasn't 'really ' FUNNY.
Sorry, you bought a POS.
Let's hope you didn't pay too much.

Time for a rebuild.