This 1970 movie by Billy Wilder is currently available on Hulu. Although it features a hetero plot, there is a suggestion of slash in the first half hour or so. A Russian ballerina wants Holmes to father her baby, and he puts her off by telling her that he and Watson are lovers. Watson is not happy about it, but there are a few nice jokes.
The rest of the movie is fairly good, and Mycroft is shown to be rather disdainful toward his brother. At one point Holmes tells his client Gabrielle Valladon that the "most affectionate woman" he ever knew was a murderess. Apparently Holmes had an affair with her, only to learn that she was stealing cyanide from his chem lab. Obviously this is a reference to "the most winning woman" he told Watson about in SIGN. Holmes also says that he was engaged to be married once, to the daughter of his violin teacher, but she died of influenza right before their wedding. This is similar to Sherlockian theories about Victor Trevor's dead sister, mentioned in GLOR. In typically misogynistic fashion, Holmes blames the woman for being "unreliable" rather than being unlucky.
The espionage plot makes a lot of sense, and the use of the Loch Ness monster to hide the secret activities is reminiscent of Stapleton using the Hound legend to kill Baskervilles. At least they were original with the love interest, and didn't try to shove Irene Adler into it. Wilder went a little over the top with Queen Victoria, with her height and her refusal to believe in threats of war, but the rest worked reasonably.
A couple of times Watson is used in a bumbling sidekick manner, but it's not too bad, and he at least is not old and doddering. He also tries his best to interfere with Holmes's cocaine use. Pretty good movie overall.