S/K/M AU search

[black-k-kat.livejournal.com]

Hello! I'm looking for a fic I read a while ago, and while I'm fairly certain it was AOS, it's possible that it was TOS. Just like it's also possible that it wasn't K/S/M, though I think my memory's reliable for that part. The fic itself was AU: McCoy wasn't best friends with Kirk, and after a (very) brief stint on the Enterprise, he was assigned to a deep space posting (I think it was for offending/insulting an admiral?). Back on the Enterprise, Kirk and Spock (maybe in an established relationship?) keep getting bleed-through from a universe where McCoy stayed on the Enterprise, and it's driving them insane trying to figure out what's behind it. (Answer, as well as I can remember it: the universe itself, because some things [like K/S/M] should always be constant.)

Wow, that's very long and yet very vague. Um. Help, please?