on a 2003 honda xr80r we just developed an oil leak. We've traced it to a destroyed oil seal behind the drive sprocket. Question is whether the oil seal can be replaced externally, or if the crankcase has to be split in order to install it? Also, we've cleaned out the torn up rubber, and round spring, that looks as if it's part of the seal. There is still a piece of black rubber that looks good. Do we remove this as well? It seems that the only thing we should see from the outside once the seal is removed, is the bearing.
thanks