Not a 550, but I have removed oil sprockets in two of my bikes and I didn't need to split the cases. 1. Remove the sprocket. 2. Get a wood screw and a hammer, and gently nail the screw into the seal. 3. Screw it in until you get a good grip, and use pliers to pull it -be careful not to pull too hard, not because of the seal but because of your knuckles. 5. Clean the seal seat and oil the inner and outer of the new seal. 6. Put the new seal into place. 7. This is the tricky bit: put the oild seal over the new one and gently tap with a rubber mallet. The idea is to drive the seal in without damaging it. It is difficult to do it because you need to hammer perpendicular, so if the seal is big, you could be better off if you have a piece of tube and use it to drive the seal in with the hammer.