Knights Who Don't Say "Ni"

Though I'm now relatively confident about writing emails in simple Japanese, I still like to paste the final result into Google translate, imperfect as it is, lest I've made some awful faux pas. There was a time at the beginning when I would write "henshi arigatou gozaimasu" (変死ありがとうございます）rather than "henji arigatou gozaimasu" (返事ありがとうございます), thus inadvertently thanking my correspondent for an unnatural death rather than their reply. It scarred me.

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.