Unfortunately with powertrain components (engine, gearboxes, transmissions, etc) more oil is almost as bad as no oil.
The leaking you are seeing is due to pressure buildup due to the lack of a natural air space. In some cases you will damage
seals and cause hydraulic lockup and may find changing speeds becomes more difficult.
The oil also behaves like a liquid
rope wrapped around the rotating components which saps
power. The more oil the less
power is available to turn the prop.