Replacing the right side crank seal is not too difficult on that bike. You can lean it over on it's left side to do it (tank off and carb drained, of course). The trick is holding the primary gear so you can remove and reinstall the primary gear bolt. I cut a piece of an old gear, about six teeth worth, and use it between the primary gear and the clutch basket gear. I've seen people jam a screwdriver between the two gears as well (shudder!!!) Don't know if I'd recommend that. Once the gear is off, pull out the collar that is behind the gear and you can then carefully remove the old seal. Be careful to not scratch the sealing surface of the crankshaft. Put some grease on the seal, inside and out, and take your time putting it in straight. You should find something that is about the same size as the outside of the seal such as a piece of PVC to drive it in. Again, take your time and keep it straight. After that, button it all back up and be sure to use some locktite on the bolt. I had the nut on a CR80 back off once and try to push itself through the case.