I haven't done anything quite that egregious for a while, but today I wanted to say that someone had been "helpful throughout". I decided that "zutto yaku ni tatsu deshita" (ずっと役に立つでした) might be the way to go. (I don't think it probably is - "yaku ni tatsu" means something more like "useful", which isn't the vibe I'm after.) However, I forgot the "ni", and ended up with "zutto yaku tatsu deshita" (ずっと役辰でした), which Google assures me means "It was a long-awaited dragon".
I don't quite know how Google came up with that, but it charms me, and makes me wish that I had occasion to write emails where that was the intended meaning.