Bendix DUAL MAG model hole in the top

I wish posting pics was easier, or I was smarter... That being said... on the Bendix 10-385124-110 model of magnetos, there are screw holes with plugs. But... on the top one of the holes in mine is NOT PLUGGED. I sorta panicked. Then I Google it looking for parts/spare plugs, I see a mag advertised - ALSO missing the same plug.

Can this possibly be for a reason? Venting etc? The un-nerving part is I can actually see the guts/gears inside. I can't imagine this is OK.

THOUGHTS?

Some of those magnetos were pressurized, that could possibly be what the hole was used for.

Mag hole

Many of the Bendix mags had just a simple black plastic plug with a flat blade screwdriver slot in it. They used a solid plug in the top hole and the same plug on the bottom, but with drilled vent holes. Any mag repair shop will have them. Ask a mechanic for a loose one they may have.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

Thanks for the feedback fellas.