Split the case?

If you have been lubricating your chain, which you should have been, that area is always going to look like that. If oil is actually dripping from that area and/or leaking fast enough to cause noticeable oil consumption, then maybe there's a problem, but just from those photos alone ... every bike I own looks way worse than that, because I oil the chain once in a while. Remember, the rest of us have nothing to go on besides the photo you posted; we don't know how (or if) you've actually established the presence of a leak. That aside ... IF there is an actual leak ...

Definitely clean up the area and clean your chain, and ride it for a bit, to establish if there is an actual problem, and where the actual source of the leak is.

IF it turns out to be the output shaft seal ...

The correct factory procedure is to split the cases because that's the only way the seal can be taken off the shaft intact. BUT. I took a look at the parts diagrams, and it's just like many other bikes. The seal appears to be held in by an interference-fit on its outer perimeter and nothing else. It's just clamped in place by the cases. You should be able to confirm this with the front sprocket removed. If the face of the seal is roughly flush with the cases around it, not recessed in behind a lip, then this is how it is.

And if that's the case ... With new seal in hand ... The old seal can be removed via determined application of a couple of sheet metal screws and vice grips. Punch (don't drill) a pilot hole to get the screw started, and jam the screw through the side of the seal, and yank it out. It may come out mangled or in pieces, and definitely damaged, but if you're replacing it ... so what. Be careful not to insert the screws too far ... you don't want to hit the bearing that is in behind that seal.

If there is ANY chance that this procedure put any metal shavings or debris into the oil, drain the engine oil and spray down that bearing with WD40 with the drain plug removed (you do not want to use WD40 as engine oil afterward!).

The new seal can be pressed in with a suitable big socket or fabricated tool to push it in along its outer diameter. Put a thin coating of RTV meant for crankcase sealing on the outer diameter of the seal before pushing it in, and be careful to push the seal in evenly all around, and don't push it in too far.

You may have to find an actual independent mechanic who fixes stuff, to follow this non-factory-service-manual procedure, because this is definitely not "by the book".