Hello!
Sorry to oppose you here, Pete.
At least later 280 SLs had their trunk (= boot) area not in "satin black" anymore. They were finished in "7164 tiefdunkelgrau" (as far as my number memory is correct), a very dark grey almost black paint code that also my 1971 230 sedan has.
Early SLs are clearly satin to semi-gloss black like all 230ies.
I don't know when the paint code change was made ... during 250 or maybe early 280 production run ...
I remember that at least one of your 250ies is completely original, so it seems that all 250 SL had the semi-gloss black trunk area as well.
Best,
Achim
(Magdeburg, Germany)