We searched over several months (January through April) for this
letterbox, and are fairly sure it is gone. Large boulders were moved
there this winter, in addition to chipping, etc.

We even checked a 130 degree "relative bearing" -- i.e., when facing
south, turn 130 degrees to your right. If you do that -- bingo -- you
find the geocache. There is nowhere anywhere near magnetic 130
degrees (or true 130) where you can get to the seawall in the alloted
paces, large or small. Having said all this, we are sure the box is
gone.