The screw is under that metal "can" right there on top of the ALDA. Peel off the can (rather agressively) and it's underneath. Yours has NEVER been adjusted, we can assume, so you may get a very nice result after 19 yrs. of having a "spinster" ALDA.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)