It looked like I was getting a slight leak around the sight glass. I had noticed some oily grime accumulate around the glass, and a little decrease in oil level over many miles. Then I started noticing some oil drips underneath, just in back of the sight glass site. I wanted to replace the o-ring, something I had done on my 1100, years ago. However, it's difficult to remove the glass--the exhaust pipes prevent full withdrawal of the attaching bolt, especially the bottom one. I've never removed the exhaust before, and the manual doesn't say much about it, as well as nothing about replacing the o-ring.