When you changed the oil, did you also change the oil in the gearbox ? If so, was the drain plug just a bit "fuzzy", or did you notice any chunks ?
Color of gearbox oil that came out ?
These bikes do not shift with the slickness of practically any Japanese bike, but they do generally pretty well, given they are rather overbuilt in most aspects.
Like Ed mentioned, sometimes if my bike doesn't drop into first I let the clutch out a bit and pull it back in again - seems to get the shafts/gears aligned and then it clunks its way into 1st without much effort. I find riding an airhead that shifting is best done more slowly deliberately, and while moving - shifting down into first while completely stopped at a light is always a bit harder than while still rolling into the the stop.