It sounds a lot like mine. 2008 model but only 3,000kms. I changed the oil and filter and the old oil was like black water. The new oil went black pretty quickly so I changed it again after another 300 miles and the new oil has stayed cleaner looking. Anyway, I have noticed that the thing seems to sort of be self cleaning itself and the gear changing is getting smoother, especially the neutral to first change. I also put in a magnetic drain plug and filter magnet so try and catch any wear debris. As for the bogging down at low revs, they are a bit like that even when they're running tip top I think. It took me a while to adjust my riding style so that I was in the right gear coming out of corners and still misjudge it a bit sometimes and have to slip the clutch a tiny bit to get past that low rev "hammering" that they seem to do. I don;t think the "hammering" does any real damage but it still makes my mechanically sympathetic teeth itch. *edit* meant to mention that when I did the oil changes I also did an engine flush, basically add about 250ml of engine flush like Nulon and then let it idle for 10 mins before draining the oil. It will thin the oil and dissolve some of the sludge that builds up inside the engine.