PAA: Interesting teshuva. Feif Un once posted the following story here http://www.theyeshivaworld.com/coffeeroom/topic/lack-of-ashkenaz-siddurim#post-316187 (I actually met the Rebbe who told it over, and he confirmed to me that it’s true):
Some bochurim (including my Rebbe) were traveling with R’ Aharon to a simcha. On the way, they stopped at a nearby shul to daven mincha. The shul davened nusach sfard. R’ Aharon asked if he could daven for the amud, and they said yes. He walked up, and davened nusach Ashkenaz.
Afterward, one of his students asked him why he did this, if the minhag hamakom was to daven sfard. He replied, “Minhag hamakom is proper at times, but this is the proper nusach!”