I'm unfamiliar with the specifics of your bike so this is a bit generic. Yes it's oil. You ought to be able to see the interior of the crankcase through the holes in the rotor. Also, there ought to be a jet in the crankcase that sprays oil through the rotor holes onto the stator to cool it. Normally I wouldn't think it necessary to change the oil but your stator looks grim enough to make me wonder if it was affecting the oil. If there is any evidence of flakes coming off the stator, that stuff could end up clogging the screen in the strainer, which would not be good. It's a hassle but you might want to pull the pan and inspect the strainer. There probably are sealing washers used for some of the screws that mount the cover. They are associated with holes that run into the crankcase. It's prudent to replace them as they may be a source of leaks. A step beyond that is to apply a low strength thread lock (Loctite 222) to those screws to act as a sealant. The existing cover looks OK - or am I missing something?