Yeah, this is something I did before. I got a wide open area and twisted the throttle as much as ever. Then I noticed the splooge, and the silencer smoking, like it was on fire. Wow, I must be rich or mixture is bad or even the 2stroke oil isn't burning off.
Don't worry. I usually clean and seal the exhaust bushing with silicone. Repack silencer on occasion. The rubber that joins the pipe and silencer shouldn't be leaking on the swing arm. Don't change jetting because of splooge. Any time you are idling around or riding in the tight stuff, you might be collecting oil. Then opening it up will blow out the excess, and it'll be on the fender. Eventually the silencer can get loaded up and really seem like a problem, but its really no big deal for jetting.
Better oils, or "leaner" ratios might help, fresh well-mixed fuel and all that too, but the oil is the cylinder lube, so you are fine as long as the splooge isn't clogging the powervalves.