I have a 71 108 280SE and I can access the antenna by removing the AC blower motor located in the RH passengers footwell. There are a couple of "hidden" bolts (hard to see but they are there), remove them and the blower will pull straight out. You can then reach (not easy!) thru the blower hole and get to the antenna. Hope this helps.

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Jerry -
If you don't learn something new every day, you aren't paying attention!!
1971 108 280SE 2.8 "Ronnie"
1985 300TDT (76,904 Original miles ) "Sadie" (Sold-went back to Arkansas)
1984 300DT "Green-go" (Sold)
1984 300DT "Silver Bullet" (Sold)
1956 220S Ponton
1985 300D (Sold)
1984 300D