Purpose of those brass colored covers on the right side of the engine block?

[RPSchuetz]

I'm currently installing a new stainless steel muffler and a new transmission in my 280SL. In getting down into the engine, it appears the rearmost small triangular shaped cover on the right side of the engine block is leaking a bit. I've secured a replacement gasket for it but before tearing into it I'm wondering what those various covers are for on that side. I'm attaching a screenshot from the Bud's Benz engine webpage that shows a clean example of what I'm referring to....

[Benz Dr.]

From what I was told by an expert those are similar to freeze plugs. Not for preventing a cracked block should you leave plain water in it and it freezes, but are actually there to let heat out during the original casting process. 

[Tyler S]

These are also used to flush the sand from the engine block after casting. The M130 engines have extra cooling jackets between the cylinders and access was needed for machining and or inspection. Those jackets have a pretty tight tolerance. 
Earlier engines (m127,129) do not have these covers. Just the 2 large openings.

[Tomnistuff]

I would agree that they are where the cylinder block water jacket core supports came through the space that would become the wall of the block during casting and leave holes to be machined and plugged with plates after sand removal.  In other words, as Tyler S and Benz Dr. say, "for core sand removal / freeze plugs" (maybe also outgassing during casting).

Mercedes tends to do things differently (more expensively).

Tom Kizer

[wwheeler]

FYI. The covers and screws are steel and plated with a yellow zinc resembling brass. Also be careful removing the screws that hold the covers on. They can be seized by corrosion and snap off. Be sure to apply an anti-seize on the screw threads during installation to prevent corrosion in the future.