When the piston moves down from the top of the cylinder presure is created in the crankcase pushing fuel out of nearly every opening in the engine. A little fuel and oil is needed to lubricate the front crankshaft bearing and some may escape out the front. If a lot escapes out the front that is not a good sign but there isn't much that can be done. It makes for eratic tuning just like a loose backplate would. The engine tuning varies from cold to hot etc.

Use Hi-temp silicone to seal muffler, and backplate - O-ring to seal carb and not much can be done about the front bearing in terms of sealing it.