High fuel consumption.

One of my engines has been using more fuel than the others for the same flight time. There has been a lot of castor oil residue on the wing after each flight. I changed the glow plug today and got in a test flight and a full tank flight with the excess oil on the wing after the flight as usual. There also was a difference in engine speed from upright and inverted flight which can be cured by adjusting the vent tube inside the tank. At home I found that I had to take the tank apart to get the tubes in the right locations. For some reason I pressurized the tank and found a leak at the screw that seals the tank. The cap is deforming as I tighten the screw and that is letting air or fuel to escape from under the screw head. I used a cap from another brand of tank and got the leak plugged. Maybe I'll test it later today as the engine run will be a lot different and more predictable without the leak. It should mean a cleaner plane also.