Oil vent trap

Hmm, what do you have coming out of the tube?

some engine oil sprinkles out now and then

check your vent tube has the small notch cut into it as called out in the installation manual.  Low pressure when flying at the end of the tube may draw out oil drops otherwise.  Don't fill to the max line. 

When flying the vent tube allows the air in the tank to exit the tank. Remember that heating the oil to the proper operating temp is getting rid of contaminants like moisture. You will have a very tiny amount of vapors which may condense into a tad of liquid form upon exiting the tube. This is in all our engines and is normal and not a big deal. It's the nature of the system and has been for decades.