Vibration
My problem: I have a new RV12 with a 912 ULS (10 hours total time). I experience a significant vibration between 3000-4800 RPM that is minimal/not present outside this range. When running the engine between 3000-4800 RPM, EGT difference (CYL 3 and 4) consistently widens to >120 F. Otherwise it is < 25 F. All engine parameters remain "in the green". Carbs have been synched, and prop blades are within 0.1 degree. Gearbox friction torque is 34 foot pounds. After my last flight, I noticed a very small amount of oil had apparently leaked from the gearbox seals (not sure which one) onto the pitot tube, which runs through the gearbox on an RV12.
Any thoughts on how to sort this out, and next steps would be greatly appreciated!