Not an expert but I understood the oil breather (which comes up under/ behind the air filter) was for engine oil not the bevel box - where you see the "leak"?
I had a leak from one of the push-rod covers which led to oil all over everything below this - engine mountings, number plate etc. My dealer has checked this, emailed pics to the factory and now ordered a new seal. Originally he thought it was coming down from the air filter/ oil breather though, as he said he often sees this.
