Baffling

[Chippster1]

Does anyone know what this oval hole above rear cylinders is for, and should I seal it?

 

[Ironflight]

That’s for your socket extension to go through when removing spark plugs. many just use a socket with a hex head top and a crow’s wrench adapter to do plugs and don’t bother with the hole, so they close it up permanently. If you want to use it for spark plug removal/replacement, cover it with aluminum tape when you’re operating - its a big leak!