Looks like silicone or some other type sealant and to be honest it looks like someone has been prying at the joint.
Early CARC bikes through to about 2010 some time just had the bevelbox bolted to the swingarm with no sealant applied. The theory being I suppose that the rubber boot and it's retainer plate would be compressed sufficiently to prevent weepage when the box was bolted on tight. While this was generally true there was a tendency for there to be sufficient seepage to cause a stain at the joint and enough people pissed and moaned that the factory started glueing the boxes on with litres of silastic. That cured the seepage but it makes the bevelbox a lot harder to get off!
My guess is your earlier bike was owned by a pisser and moaner and his shop, or he/she addressed the issue by applying gobs of silicone sealant of their own. Note that if the bevelbox pinion seal or gearbox output shaft seal goes the tell tale is oil dripping from the brake hose clip closest to the joint on the swingarm. Rarely will it manifest itself as a leak at the joint itself.
Check the bevelbox oil level. It should be at the bottom of the threads of the filler port. Unless it needs a lot adding stop worrying and just ride the bloody thing.