Both are possibilities.  See archive message 64583, Jan 13, 2019.

Steve Boese

> On Mar 4, 2021, at 12:51 AM, Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:
>
> Whats the downside to the drive filling with oil?
> Pressurising the beast and its seals?
> Is there more frictional losses and heat?
>
> Steve Izett
>
>> On 4 Mar 2021, at 2:35 pm, Sboese sboese@uwyo.edu <flyrotary@lancaironline.net> wrote:
>>
>> Finn,
>>
>> When I installed a vent in the top of my RD-1C drive it acted as an additional drain.  The drive operated completely filled with oil until the size of the original rear drain was increased to an ID of ~5/8” (1/2” NPT pipe).
>>
>> Steve Boese