I use the Kayfun 3.1 and the Kayfun is supposed to be a clone of the Russian. On my Kayfun there's a collector area under the coil deck that holds
juice that drips around the coil area. That can drip if you don't blow it out or disassemble it when you rebuild. Your Russian probably doesn't have the collector, just the air adjustment and the air hole.
There's also an air adjustment screw next to the air intake that can drip after a fill or when the collector gets full. Other than O-rings not sealing those would be the only sources of leaking I know of.
As Izan mentioned, leaking after a fill sometimes happens. I blow mine out as described below after I fill.
Try blowing it out into a paper towel through the drip tip while holding it tilted with the 510 thread end high. If you hold it level you might just blow the contents of the tank into the towel through the chimney feee slots! The air intake hole should be facing downward toward the towel. If you get some
juice out of the air hole, you will probably solve the problem. It would be juice that collects around the coil inside and makes it's way into the air hole. Doing that on the Kayfun 3.1 also clears the juice out of the collector cap where the 510 thread is without removing it.