C280 Oil leak and photos

[recruiting]

I have a few questions i hope can be answered here. I have included pictures below for for interest.

1) How can i tell or DX if I have a head gasket leak?

Symptoms: minor leak REAR of the engine ( cant see as it is to close to the fire wall) oil hitting hot muffler when driving on highway ONLY. Street driving will not produce leakage. I do not see anything but oil on the ground.

2) Have you folks done this gasket replacement on your own? How long and complicated will this be should i decide to do it? I do most engine work myself and I own a torque wrench...

3) now the pictures. I also have a small leak up front. what is this ROUND part with the plug in the picture that is leaking oil on that hose? Would fixing this be tough as i dont even know what it is?

4) If you have done the head gasket replacement, what should I look out for when doing this and how much time will it take..