I've had this issue.
A few things to note - if it is a small leak, many times there will be no drippage on the ground because the drip will evaporate after hitting the exhaust. You can detect the smell but can't see smoke in daylight. In dark, bike hot, stand back and shine flashlight beam thru the air space above that side of bike and you may see smoke.
Oil will be more likely to drip out if bike is parked using the sidestand because the hot oil will then submerge the seal area. With bike level on sidestand the oil level may not reach the seal if the oil level is lower than the top of your window.
I used a socket which was slightly larger than the inner side of the outer ring, and the socket had a slight taper on the outside edge. I used a vice and gently pressed the socket into the seal a little to expand the outside sealing surface slightly, and then pressed the seal into the pump. I verified the O.D. of seal had been expanded by checking with calipers.
You don't have to drain engine oil to change seal, IF you are careful and lean the bike to the right some. Not real far, just far enough to get the oil level window to show no oil, or approx. Been a few years so can't remember exactly how far I had to lean it. Anyhow, leave the bike in gear, block the tires and then hook a tie down strap from the left handlebar to something solid, then begin to lean bike to right. I also had the wall or something on the right side to catch the bike just in case but it wasn't an issue.
