An oil leak there is not uncommon on any KTM and is an easy fix... If you slide off the front sprocket there is a bushing behind it that rides against the outer counter shaft seal, this bushing can be easily slid off by hand.. Between this bushing and the countershaft bearing is a 25mm x 2mm o-ring {maybe bigger on the new bikes} that seals the inner countershaft.. So it works like this, the o-ring goes against the counterbearing, then the bushing pushes against the o-ring sealing the oil from getting through from inside the bearing.. The outside of this bushing seals against the case seal keeping oil from escaping out side the countershaft.. In order to seal the O-ring to the inside of the bushing the countershaft bolt/nut has to be correctly tensioned to hold pressure against the works.. The whole idea of this design is that instead of the case seal cutting a groove and wearing the expensive countershaft, it instead wears out the easily replaced inexpensive bushing sleeve... The o-ring is pretty much the only thing that will fail in this system and is easy to replace... Running a too tight of chain is one of the biggest reason that the little o-ring fails in the first place... As the suspension compresses to mid travel the distance from the countershaft to rear sprockets gets farther apart causing a snug chain to become tighter causing bind on the countershaft as to where it pinches and shags the o-ring.. When we have a group of riders parked around I will usually take a walk around to look at the bikes and often will spot at least a couple bikes where I recommend the owner add some slack to the chain.. I see bikes come out of dealer service with the chains to tight.. On my bike the same O-ring that fits behind the countershaft bushing also fits the clutch slave cylinder so I carry a couple on each trip to perform double duty, though I never remember having to change one in the field.. I put on a new countershaft O-ring seal every time I change out a worn countershaft sprocket, seems to be a good practice as the seal seems to hold for the life of the sprocket..