Couple of years and every time I check. About 10 times thus far. Do I have a special bike that doesn't hide oil?
Very likely that you have simply never looked in the same particular order that the OP has as well as many others that have seen the disappearing oil... The best of my memory serves it up something like this. Owner checked or changed the oil with bike on CS and then let the bike sit overnight or longer and on checking the sight-glass again and did not see the oil... Freaking out they add oil to the engine without starting and then re-checking; they then end up with an overfull bike that covers the sight-glass to which starts another thread saying that the sight-glass is a worthless POS....