What does this port/hole do?

[timbrass]

Any idea what this port/hole on the side of the Transmission does? Should it be covered with a plug?

I believe it is an Allison 2000 Transmission on a DT466e

Whilst sorting out the rust I spotted this port/hole on the side of the transmission? You can see "toothed gearing" inside. Doesn't seem right that this is exposed to the open air! Also surely Transmission Oil could escape from it?

On the other hand it doesn't have a thread on the inside of the hole to take a screw in plug....

Should I leave it as it is or plug the hole somehow?

2nd photo take from ground level underneath the passenger door.

[2kool4skool]

That hole is in the bell housing / convertor housing. No harm.

[Docsgsxr]

I am no allison mechanic, but I am very confident it is an inspection port.

[timbrass]

Thanks. I decided I needed to know a bit more about Transmissions so I watched this!

https://www.youtube.com/watch?v=8xFwoTCInY8