I inspected the holes for my sunroof drains on my '85 300d (when I still owned it). I poured some water in slowly into the holes. The rear holes drained behind the rear window. There is a trim piece that kinda looks like a fin. I couldn't see the exact exit hole but the water came out freely and drained nicely.

I don't remember exactly where the front holes drained to. I was trying to find the source of my dreaded rear passenger footwell flood. The sunroof drains were not clogged as afar as I saw cuz I didnt get any water in the footwell when I tested these drains.

Sorry, I couldn't be of more help.

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Frank
84 500SEL EURO 101K ( JUST LIKE MY 1ST WIFE. GLAD TO GET RID OF HER! )
85 300D 310K (sold)
90 350SDL 184K sold
83 300D 118K (sold)
88 300E 153k (sold)
93 400E 105K (sold)