Correction.
Rav Moshe’s opinion on chalav hacomapnies is clearly printed. It is muttar according to the law. (This is not a chidush if you know the sugya. The Chazon Ish agrees.) One is allowed to be machmer. If it comparably priced and not difficult to ascertain, one should be machmer. If one was makpid and the price went up, he must continue to be machmir.
Saying Rav Moshe had a kula here, is on par with saying that he allowed an Eruv In Brooklyn.
Yoshon was not kept for centuries in Europe. It is not clear why they didn’t, but such a precedent is not called a kulah. The same goes for birkas hamazon with a cup of wine. Today, some yeshivaliet want to be makpid on everything. They are completely mistaken about everything. One has to be really big and really know what they are doing to revive a practice that was dormant for centuries.
In the Yeshiva of old, even top lomdim were consistently being knocked off their high horses because there where real gaonim in almost every beis medrash. In such an atmosphere, one trembled at the mere thought of changing the minhag. Today, the cream of the crop run to their private offices to learn, and the masses of the yeshiva are left at the mercy of the lunatics who think they know everything without learning anything. In The Old Yeshivishe Velt chumros were well hidden. They were so modest about it, that their own families weren’t aware of what they were doing.