Green’s Dictionary of Slang

(orig. US) any form of sticky substance, ointment, cream.

1950		in Sat. Eve. Post 6 May 42: The company [...] sells shaving guck [HDAS].
1953		S. Bellow Augie March (1996) 178: The smells of crocodile beds of guck from the cleaned sewers.
1965		J. Thompson Texas by the Tail (1994) 27: She was eating some horrible guck out of a paper sack.
1986		S. King It (1987) 279: God knew what strange guck there might be, clinging to the smoke-blackened inner tiles. [Ibid.] 946: She was streaked with what looked like every kind of gluck in the universe.
1993		J. Mowry Six Out Seven (1994) 336: There a pan full of some nasty green guck, but be sure to step in it first, okay?