I made a sort of loosy-goosy due-diligence effort. There were really two questions here. One was: what are some example of early uses in its present sense. That's sort of a separate topic. The second is: despite the fact that there _are_ early uses in its present sense, its use exploded circa 1980 or so. Based on casual sampling, virtually all uses after 1980 are in the present figurative sense. (Before that, quite a lot of them are not). If I search _only_ for articles in which the phrase "slippery slope" appears _in the title_, the very first such reference is in 1943, and is to a literal use: "Dauntless Is the Skier Seeking Snow; The Uncertainties of Travel Fail to Halt His Quest for Slippery Slopes as Shown by a Railroad Trip to Snow Valley Above Manchester, Vt." The next nine span 1963 to 1988, and all are, I claim, I judge, I opine, the modern use. "Russia and China Edge Down a Slippery Slope;" "The Nation; U.S. and Cambodia: Down the 'Slippery Slope' Again?;" "On the Slippery Slope To Another Vietnam," etc. So, again, what would you do here? State the common-sense inference ("the very first such reference is in 1943, and is to a literal use; the next nine span 1963 to 1988 and are all the modern use," and give title, date, and page of all ten in a footnote? Surely not: put title, date, page of all ten in the article itself? With regard to the OED and first use in its present sense, why yes, I know better than that edition of the OED. First of all, William Safire gives a 1909 example in a 2002 column: "The key task of the phrasedick is to find earliest uses of ["slippery slope"] in its present sense of "a course that leads inexorably to disaster." The OED tracks it to a 1951 novel, but new retrieval technology lets us do better than that.... We have this 1857 use from Chambers' Journal: "When the educated person of the middle class is reduced to pennilessness... what but this gives him the desire to struggle again up the slippery slope of fortune?" In both of these citations, the meaning is closer to "the greasy pole...." The current sense... probably surfaced in the early 20th century, possibly in an article by a writer in a 1909 Quarterly Review, published in London: "the first step down that slippery slope at the bottom of which lies a parliamentary government." But new retrieval technology, namely Google Books, lets me do better than Safire. I found an 1878 reference by one Bernard O'Reilly: "It is not with them we are concerned: they will not be taught or reformed; so, they will go down the steep and slippery slope on which the heartless move, to perdition!" I think that's unquestionably an example of usage to mean "a course that leads inexorably to disaster." (Of course, I'd never draw such an inference; I'd just quote it and let the reader decide. The reference is: The Mirror of True Womanhood, A Book of Instruction for Women in the World, 2nd Edition, Dublin, M. H. Gill and Son, "Reprinted from the Thirteenth American Edition." p. 136." Actually the question of the year is complicated because the Google Books image is from an 1883 edition, but the 1883 edition says it's from the Thirteenth American Edition, which was published in 1878. Whether it was in earlier editions I don't know. But it's older than 1951 and by golly it's older than 1909. And I found an 1837 reference that does not actually use the phrase "slippery slope," but does say: "There are points where the Christian must always stand on guard. His danger is seldom found in gross offenses... but in small indulgences, and weak compliances, where conscience rather doubts, than condemns. These gradually draw him nearer and nearer to the world, till the line of separation is lost. Many a Christian has glided down this slope to perdition." Osler, Edward (1837), Church and King," Smith, Elder and Co., London, p. 13