There are small holes at the bottom of the rear door openings....towards the rear just above the sill.
Little rectangular rubber plugs push into these holes. They're sold as 'Door Pillar Check Valve Grommets':
https://www.ebay.com.au/...27c79:g:BT0AAOSwUp1gUuzp

Mine were missing, so I ordered replacements. I expected the plug to have some sort of 1-way valve in it, but no.
They are just a solid rubber plug. No hole or slit.

My question are:
1. Should there be a slit/hole in these plugs ?
2. What are the holes for ? If they're supposed to be filled with a solid rubber plug, why have the hole at all ?

Thanks.
Andrew.