Water pump seal is not so much a difficult job as it is time consuming. If replacing the seal you will want to make sure to put some sort of gasket sealer around the edge before you push it in place because the fit is not very tight. I used a socket with a slightly tapered end and pressed it into the seal a few times on the bench vise to expand the OD a little. Verified the expansion with calipers. Pressed it into place without sealer because it fit snugly after expanding it. You will also want to replace the two o-rings. I replaced mine without draining the oil by leaning the bike and securing it so it wouldn't roll. If your oil level is low in the window I'm not sure how much if any would come out the water pump if the bike is level.
The water pump has a weep hole. easiest way to see it is when it is dark. Use a 8x8 mirror held under the engine then shine a flashlight up into the area and the weep hole should show evidence of leaking oil if the seal is bad.
Be careful when sliding the seal over the notched end of the water pump shaft. Mine was very sharp and cut my first seal and I had to do it again, this time I sanded off the sharp edges to help prevent this.
One last thought, if oil is coming out the weep hole, it has flowed past the bearing and washed out the bearing grease. My theory anyway. Now the bearing is lubed by the engine oil which got past the seal. probably shortens the life of the bearing but I believe I've put 20,000 on my bike since I did the seal and no problem yet. Oh, I did mine around 60,000. If I had a bike with 80,000 or more and had this problem, I'd think about replacing the pump which is around $160-180 iirc.
