Hi Rybenuk,

1)The coolant reservoir actually needs to be checked from the front. I think they used the same coolant tank as the XT660R, but it is not mounted correct for the markings, so you'll see nothing at the back, important that you see something in the front

2) The tube at the bottom of the airbox fills with oil if you ride the bike hard. The 08 models had this problem with it filling rather quickly, and the oil collector design was changed. But yes, you can remove the plug to drain, just be very sure to put it back, otherwise your engine will suck in dirty air through there! And obviously check your oil level if there is a lot of oil.

3) Look out for the injector wire rubbing through against the frame, there was a post about it not too long ago. Plus the radiator guard rubs through the radiator in time, also a recent post (I've still got to check mine!).