My 1978 300CD has the flat blind drain plugs installed in all of the rocker positions. I fixed a lot of rust in this area, and was somewhat surprised that no way to drain was designed into this cavity. I've since noticed on several sites that a lot of w123's, including another 78 300CD, had the banana shaped open plugs installed on the rockers at the midway point beneath the seats. Perhaps they were only installed on vehicles with a sunroof (even though I don't think the water drains in there)? I'm contemplating installing a couple to prevent future water issues. Anyone familiar with the history on these and why mine might have been MIA? FWIW the plugs in this location were still covered with the vinyl undercoating indicating they were original.

See attached picture of said plug(not mine).

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Those sure look like they should drain.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

These are drain plugs but not drain plugs for you!

They were used during the manufacturing process when the body received an e-coating. After the e-coating and main body paint was applied they fitted the "drain plugs" and then smeared that stupid undercoating junk on the underside to make sure that any leak / water ingress from the inside of the car spreads out as far as possible due to capillary action...

...wonderful system...

...fantastic idea...

...0/10 Mercedes - see me after school...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

These are the same plugs on my 97 C280 with a sun roof.

The factory sun roof drain rubber hoses end _inside the rocker_ then drain through these holes. When I had the head liner removed I got new hoses ( dealer ) then routed them through theses plugs. ( The replacement hoses are cut to fit and were about 2 ft longer than stock )

If you don't have a sun roof and can prevent water from entering the rockers, I'd seal them up and flood the rocker with rust proofing ( waxy stuff not hard undercoat ) If you can get the rocker sealed, I would leave some holes into the passenger compartment so the rocker can dry out if some water gets in.