Ah. So, looking back, when you wrote that "in your sentence "Now it's sunk", the verb is is and sunk is an adjective not a verb" you are referring to the most likely reading of RSL's actual sentence rather than asserting that "it's" in the phrase "it's sunk" is correct only as a contraction of "it is" and would be wrong as a contraction of "it has"?
Ok, ok, I hear the silent screaming. I'll go away now.