Green’s Dictionary of Slang

a whinger, a complainer; thus mizzle v., to complain.

1894		Bunyip Gawler, SA) 26 Jan. 2/4: You can bet your life the grizzler/ In the end will be a mizzler, / A duffer hardly worthy of a kick.
1945		Baker Aus. Lang. 134: To complain: to mizzle and to whinge (whence come the nouns mizzler and whinger, and the verbal nouns mizzling and whingeing).
1948		R. Raven-Hart Canoe in Aus. 66: To ‘mizzle’ was to complain, moan about something.