Plug in wing-root vent?

[Red Air Rambo]

Mines a 73 and just 1 hole each side no plugs. Hope to look at a 78 tomorrow and will let you know. Talked to my A & P and he could think of no reason for the plug unless to restrict cooling. Kinda like Truckers in the winter time with their radiator shields. I'll look at the 78, then get in the manuals.