Looking for a fic

[classicdrogn]

This one was either a short or a short segment of a compilation, and I'm pretty sure listed under "surprise crossovers" so I'm not having much luck, having forgotten the title and author - though it might not have been BtVS based, I'm pretty sure it was, and was on TtH. Anyway, an old guy shows up at the door of (again, pretty sure) the post-series slayer school/headquarters, saying there's something bad coming and he just knew he had to be there. He's always had a sense for it, you see, back in the army he thought he was just hearing helicopters approaching, but as time went on he's realized there's more to it, and now it's so strong he's afraid something really calamitous is in the wings.

le tweest

Turns out he's Walter "Radar" O'Reilly, once of the 4077th MASH.