This past weekend I was reading through the Torah Temimah on Vayikra and a paradox occurred to me.
The Zaken Mamre is specifically applied to one who is in a position of authority over a community. If he preaches to his followers to act against the ruling of Sanhedrin (i.e.: following Beis Shammai after the psak of Beis Hillel was establish as law), then he is first warned and later executed for contravening the courts.
Conversely, the Par He'elem Davar Shel Tzibbur is a communal sacrifice brought because the Sanhedrin made a mistake in psak that lead to a large number of individuals (the specifics aren't important in this question) committing a sin that is chayiv kares. In this case, someone who knows the proper halacha is not "exempted" as the rest of the congregation, since he knows they ruled improperly, IIRC.
BUT it would seem that we have a contradiction - if the Zaken KNEW the ruling was incorrect, he cannot follow it, but it would ALSO appear that preventing OTHERS from following that mistaken ruling (to prevent a case of lifnei eiver) would lead to him becoming a Zaken Mamre!
In fact, this would seem to be the precise issue of Tanur shel Achnai (and later tanur ben Dinai), where one shittah held it was tamei and the other held it was tahor - the side holding it was tahor would potentially lead to someone bringing tumah into the Beis Hamikdash, an issur kares!
Taken to a logical conclusion, Beis Shammai would be required to "shut down" it's yeshivah once it was paskened that the halacha was no longer like them, since continuing to teach their halachic mesora would lead to Zaken Mamre, yet we see that Beis Hillel and Shammai did taharos "on top of one another" - that Beis Shammai continued to practice according to their mesorah!
Are there sources that deal with the tension between these two conflicting principles? And what are the boundaries of Zaken Mamre vs. the Moreh Halacha who (it would seem) must teach others to prevent the mass violation of halacha?