Ehaust oil leakage ?

You need to lean out the carb jetting a little. And before someone jumps in advising you to change your gas/oil ratio I will say That IS not how to cure this problem. Also make sure you are running with a clean properly oiled filter

Doing those 2 small step will help unleash some extra power and crisp throttle you never knew was there

It's normal for the CR85 to have that at the cylinder/expansion chanber junction. There are a couple ways to fix it. You can get an aftermarket manifold with O-ring seals (Swede Tech makes a really nice one) which is the best solution. Or you can get a new OEM seal and clean both the expansion chamber and the manifold REALLY well and install it and hope it seals well or just pop some high temp silicone on when you put the new seal on and it will be sealed for sure. You also need to make sure your springs are good and tight to ensure a good tight fit.