Saginaw 3 speed help

[hughesracing9]

switching transmissions to one that Ive run before and had no issues. I noticed there is an open threaded hole under the 2/3 shifter. Neutral switch im guessing? my other two sags dont have anything so i cant take it off of one and on to the other.
Any one know what it is? does it leak oil if not plugged? cant imagine it failing out while sitting on the shop floor and i ran it plenty of times and never leaked

[r3tracing]

Change the whole side cover