I need an specific advice on a specific area (not the main one) in my PhD research (e.g. is it a good idea to include the factor x in the review and analysis of the topic y?).
As far as I know, my supervisor is not an 'expert' in this specific area.
I think that someone else, who has recently done a PhD in my department and has good connections with my supervisor, is an expert in that area and can help.
In academic etiquette: should I make my supervisor aware that I am asking an advice from that person?