The old carbie girls are NOT well known for oil consumption. I've owned 3 (2 currently) and never have to drop an ounce in either of them, even after a thorough drubbing (well, relatively speaking, as
will surely not corroborate that), but you get the idea. Now, that's not say that yours has a thirst for oil. It could, but there would be subtle clues. Wet, black tail pipe, sooty exhaust smoke, and most importantly NOISE
. If you report a low level, but she runs like a top, I say she's good to go. Do as Unlsow1 recommended though, get some fresh "cheaper" oil in there and flush it out 2-3 times. It may take a bit to get the window clear, and the only way really to clean it out nicely would be to remove the clutch cover. Anyhow, let us know how it works out. Unless the bike was treated badly with only being 1/2 full of oil, I think you're gonna be OK.