I have a bad oil leak somewhere around the back of the engine, and I cant see where it is.

Its a 4x4 and as you probably know the filter is at the front, almost under the radiator.
I just put new hoses in for the oil filter cause I had a leak in one, come to find out there is another leak somewhere.
A friend of mine who is a mechanic says its the intake manifold gasket, there plastic crap and I just had to get it replaced last year because it was leaking anti-freeze, also I never knew oil came through the intake manifold.
There is also a oil sending unit back there that I managed to get my finger and rub around it, and it was clean. So what do you guys think, valve cover or intake manifold? and if there is something I'm missing or not aware of please tell me. Any info or suggestions are greatly appreciated.

 

Take a flashlight and a mechanic's mirror and take a good look around the back of the engine. My suspicion is valve cover, but you won't know until you can see back there.

 

Thanks, I don't know why I didn't think of that.