Here's the answer I'm sorry that sick is NOT wrong, but it is not, and neither, in a sense, is "seek."
The word is "sick," not necessarily "sic," according to the Oxford English Dictionary. However, "sic" is also listed ("Also sic"). It turns out that in either form it is dialect, and a variation of Seek! [But the main listing is "sick," with "sic" as an alternative, and no independent listing for "sic"]
I too would have thought it "sic," but you have to keep an open mind in these things since what we are used to and comfortable with, is what we tend to think is "right." But what is right and what we do has very little necessary relation.
Here is the dictionary definition and spelling:
"Sick:"
"Also sic. [dial. var. of SEEK v.]
1. trans. Of a dog: To set upon, attack (an animal). Chiefly in imperative.
2. a. To incite or encourage (a person) to attack. Const. with on adv. or prep. Also, to set (a dog or other animal) on or at.
b. fig. To set (a person) to work on; to set (a person) to pursue, observe, accompany, etc. (const. on or on to)."