Oil can leak onto the LIM. Typically in the recessed areas where the bolts are located. This is because the bolts are threaded into the heads wehre coolant and oil ports are located. Oil is less common as it'* not under pressure, but it can seep up there. Did on my car
The best piece of advice we can give you is to replace the UIM when you do this job. The UIM has a weakness in the area where the coolant goes past the EGR tube and into the throttle body. Over many heat cycles the expansion and contraction of the EGR area cracks the one layer of plastic (the manifold is a nylon aka plastic) that seperates the coolant from teh EGR. Then the coolant is in the intake manifold. Down the road this leaks to hydrolocking. Rockauto has about the best price after forum discount code.