While it does appear that there was some dirt that may have gotten into your intake and mixed with the oil there, it's mostly perfectly normal. A little dust from a dirty air filter can look like a huge problem. The CDR puts excess crankcase gasses back into the intake to be burned again. These engines have a lot of blow by which, in turn, causes a lot of crankcase gasses, all by design (for whatever reason). There will always be some oil mist mixed in with your crankcase gasses no matter what engine you have. That is just a "mechanical law".
Don't worry about what is sitting on the bottom of the intake manifold. The damaging part has long been run through the engine. What's left over now hasn't gone anywhere, maybe for years. You can remove the intake and clean it out if you want to, but I wouldn't get too excited over doing it unless you really want to.
As for that clip, it doesn't look like any part of the engine that I can think of. It probably got dropped by accident and ended up there. I've seen MANY nuts and washers from the IP under or behind the intake. I've even seen several bolts there too. Even though it was under a radiator, I once found a brass (looking) wrench that was dropped and never found.
I don't believe that it's possible for oil to leak from under the intake manifold since there's no liquid of any kind that runs through it. It is possible that oil could seep from under the front or back edges of the valley pan if it's not properly sealed down. Is that where you saw some oil coming from? If it is, you ca remove the manifold and the valley pan (intake gasket) and reseal it. These days, they aren't available new right now (unless something's changed and I'm not aware of it). You can clean up your current one and reuse it.
