Its my first nitro rc (hsp backwash) with a vx-18 engine. I am still in the break in procedure, so im running it sloppy rich. But its leaking fuel from behind the flywheel. Its brownish so not clean nitro (i was quite suprised). Is it a common problem? I am really suprised because its a new engine.

No need to worry, due the rich setting it is normal some oil is pushed out through the front bearing. When the break-in is finished and the engine is tuned right it will be gone or for sure much less.