If the flywheel nut has loosened up, you could see it by looking in the inspection port on the left side - but not a problem with the 998's. There have been a couple of cases of testastretta rockers flaking - but not many.
For the first few oil changes, you'll find all kinds of crap floating about in the motor and lodging in the screen or depositing themselves on the drain plug. "manufacturing swarf" is the technical term for this detritus. metal bits leftover from machining and not cleaned out, excess gasket sealant that breaks off, thin metal sections from the castings that break off.....lots of stuff.
I'd change the oil and not worry about it, then take it in for the service. just keep an eye out at oil changes.