When I try to use the 'Advanced Search' to look specifically for 'W' fare class (40 PlusPoint upgrade), I do not get the 'Requested Fare Class' column across any of the flight options. I called in to the United 1-800 number, and for whatever reason they say you can't price this route in W - across any of the flight combos?

It is a regular round-trip route, so I am surprised, and is no different than how I have booked in the past. Is there a special rule around W fare class only opening within X days of travel that I may be overlooking? Thanks for any tips!