I think this may be because it's a bit of an orthographic anomaly in English.
It's a bit funny to see a word deriving from Old French (hence the 'au' spelling) with an English -d stuck on the end of it, as well as a preceding 'g' at the start).
Also, I think this verb tends to be used most commonly in its infinitive form, as opposed to in the past tense (e.g. 'it can be difficult to gauge...'). Though, that is just my own experience.
It is grammatically correct, as you said.
Edit: Also, I agree, it sounds a bit off in the context presented.