I've owned a lot of two stroke dirt bikes and some drooling or spooge is normal. Basically it is just unburned oil from combustion. Some people have minimized it by experimenting with mixture ratios. Like going from 32:1 to 40:1 or rejetting the carb. Also, you are more likely to get spooge if you are running full synthetic premix oil. Even how you ride can cause it. Going too slow or lugging it while out riding and not keeping it on the pipe because it doesn't allow for consistent exhaust pipe temperature where the stuff will be burned off. In a worse case you could have worn out piston rings.
I used to have the problem with my Honda CR250. I experimented with jetting and was able to minimize it. Then I found out that Honda had a bad design on the exhaust flange so I replaced it with a CNC machined one from Boyesen. That helped the leak at the pipe header but eventually I could still see drooling at the tail pipe at the silencer. Even with a new Wiseco piston and rings I still had it.
Later I decided to mod by adding VForce3 reeds and a Pro Circuit Platinum pipe. Did some minor jetting changes like the pilot, needle and main jet due to the mods. I haven't had any problems with spooge ever since. The spark plug looks perfect after taking a reading.
BTW - The Yamaha WR250 and Honda CR250 are notorious for jetting problems. Normally too rich.
Also, I had experimented with spark plug heat ranges and it didn't help much.