Are you filling the engine with the correct amount of oil ?
Common mistake is not to screw the dip stick in when measuring the oil level.
This has the oil level in the sump at or higher than the top of the dip stick tube casting so it will always leak.
The dip stick tube is HDPE which is a bad choice of materials as it a thermo plastic deforms when it gets hot so is not stiff enough where the O ring sits to maintain an oil tight seal.
Have you checked the governor shaft ?
On commercial mowers the shaft floggs the hole oval due to the number of operating hours.