With 29 occurrences in OhioLINK, today's word has a bit of an identity crisis, since not everyone considers it to be a typo at all. According to Wikipedia: "Some individuals may prefer to spell transsexual with only one s, thus writing transexual. They will typically assert that they are attempting to divorce the word from the realm of psychiatry and medicine and place it in the realm of identity." Although, frankly, this makes no sense to me. How does spelling it with one s make it less of a medical matter and more of an identity issue? It only seems to make it less semantically correct, since trans- is an established prefix and "tran-" isn't. At any rate, this is clearly one case in which you must consult your primary source. Whether or not you then choose to regard it as a "sic-ness" may be left to your own discretion.
(Portrait of a young Gore Vidal, author of the 1968 novel Myra Breckinridge, by Harlem Renaissance photographer Carl Van Vechten, from Wikimedia Commons.)