Additional Bracha at End of Maariv
One who has the minhag not to recite the additional bracha at the end of Mariv [ברוך ה’ לעולם] finds himself in a minyan which is sayin it. This is common when someone from Isrel visites abroad. Should he recite it with the minyan?
The minhag not to recite this bracha is to be concerned for the opinion in the rishonim who hold this bracha constitutes a hefsek between geula and tefilla. That being the case Igros Moshe [O:C 2:102] rules, that one should maintain his custom and even in a minyan which recites the bracha, he should refrain. He should do so in an unassuming way so as not to draw attention to the fact that he is not davening along with the tzibur.