Mishna 16: What Are Rabbis For?

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“Rabban Gamliel said, make for yourself a rabbi, remove yourself from doubt, and do not give extra tithes due to estimation.”
Rabbi Dovid Rosenfeld comments on the above Mishna from Pirkei Avot at:
http://torah.org/learning/pirkei-avos-chapter1-16/

He makes one statement in the article which I don't feel totally comfortable with.
He says:

Equally important, one should adopt a single rabbi rather than choosing from an assortment. Many people are in the bad habit today of “shopping around” for opinions, searching until they find a leniency — or a stringency (takes all kinds, you know). The ideal, however, is to select a single and proper mentor for yourself

Just as in the world  of medicine, one doctor might be a specialist for a particular organ of the body and his opinion takes precedence (for that organ of the body) more than the opinion of a general Doctor, it is quite common to have a specialist in particular areas of Jewish Law (Halacha) where in this area, that specialist is the best person to consult, rather then relying on just one rabbi, who might not be a specialist, in the area of halacha that you are interested in clarifying.
To put this in more real terms, it could be that certain non-zionist Rabbis "knew more Torah" in general than someone like Rabbi Kahane, but on the issues that Rabbi Kahane specialized on them, he knew more and was the real authority.
Even disregarding the issue of the specialist in halacha vs the non-specialist, there are additional situations where it might be advisable not just to stick to one rabbi, but hopefully someone else will fill in some of the details I left out in this post.