On a rebuilt 582, after the hour-long break-in period and a few minutes of additional running on the ground, gearbox oil was found dripping from the bottom of the engine onto the muffler, and from there onto the nosegear tire.
The leak seemed to be coming from the bottom two bolts of the gearbox cover.
The gearbox was drained and the cover removed. No evidence of damage to the paper gasket was found. A new gasket was installed using Fuel Lube. The gearbox cover was carefully refitted. The engine was rerun for about 10 minutes, up to 5000 rpm.
Enough oil was leaking after shutdown to drip once or twice onto the asphalt. No oil was found behind the prop hub, at the top vent, at the bottom drain plug, at the side fill level screws, at the top and middle cover nuts, or at the rear where the gearbox meets the engine. Gearbox oil was found on back of the prop, about at the location of the bottom two bolts of the gearbox cover, and spread on the back of the blade from there and along the top edge of the head between the cylinders.
When the gearbox was removed from the engine, about a quarter cup of oil came out. This chamber at the rear of the gearbox is supposed to be dry.
Fuel Lube was used to retain a new o-ring in its channel on the back of the gearbox. New bottom bolts and new lockwashers on all bolts and nuts completed the installation. No leaks were found after about 15 minutes of run time, and overnight storage in the hangar.