There are some oil galley plugs throughout the engine, they are threaded and use NPT plugs. There are also galleys that return and move unpressurized oil around to keep the trans oiled and oil flowing back to the pump. If not threaded it is probably the latter.
I no longer have a MMI Manual so I can't look it up to be sure. It looks to me to be an oil source for the gears, just not sure.
Dave Neptune
