Ah, good call. But then why is there an 8 in the cave? Weird.
I kept focusing on "arm" for the third part, but I think it's supposed to be right mast (or right whatever). So maybe it's excavate/dig...eight (steps/???)...right of (???)...etc.
EDIT: Part #5 is treemail. I have no idea why I didn't get that sooner.