Some of the brown gunk on the head is what every single GZ ever has had. Best we can tell, it's the old shipping oil seeping out. It's not a serious problem.
Clean your head with foaming engine degreaser and then watch for anything new that develops.
Honestly, what you have is pretty common for the bike and not really anything to be concerned about. Keep an eye on it, obviously. And check your oil level like you should. But it looks like a bike in pretty good shape to me. Just enjoy it.
PS: If it bothers you, grad a service manual and torque all of your head bolts to spec. You're good to go.