I just learned the gemorah in Taanis 26b this morning, concerning Birkas Cohanim at Mincha and neilah on a taanis. There are 3 opinions, but the conclusion of the gemorah is a little tricky.
There is ‘Halocho’ like one opinion, then there is ‘Minhag’ like another and ‘Nohagu’ like a different way.
The explanation in short is, that even though the strict method of halachic interpretation points to one opinion, the minhag is like a second opinion. That means the way people should act in regard to this din. The gemorah says “?????? ??????” that we instruct people this way if they come and ask. Nevertheless, the people act in a different way if they don’t ask.
It seems the correct way is the ‘Minhag’ i.e. that which we are told when we ask our Rabbis, even though it may be different to the strict ‘Halocho’.