Do you have the C9S (the Regen engine with the DPF)? A C9 "ACERT" can be the 2004-2006 (without DPF) or the 2007-2010 (with the ARD, DPF, CGI, etc.).
If you remove the dipstick, can you feel (gas) pressure coming out the dipstick tube when the engine is running?
For the oil spray, One DIY check, would be to verify that the crankcase breather is not clogged/blocked. If the blow-by pressure can't get out of the crankcase through the breather it will come out somewhere else (engine seal, dipstick, etc.)
The older C9 ACERT has a breather that needs to be cleaned periodically. I don't know if the C9S breather is different from the C9 or not. Here's a snip from the C9 engine manual:
Also, I think the ECM will set a fault code if the crankcase pressure is too high - so if your not getting a code/light, then the breather may not be the issue. But it's a starting point.