Answer: A.      At first glance, he should say the prayers together with the congregation. However in the book Netivim B’Sdeh haShlichut (Section 1 P.36, comment 28) it is pointed out that that the Rebbe’s practice was to say it at his own pace, and afterwards say the 13 Midos HaRachamim alone, and it seems that this was even after everyone else had finished saying them, and not as written in certain responsa. B.      It could be that this is based on what is written in the responsa of Torah Lishma, who says: “Since he began Vidui with the congregation and the Vidui is the beginning of the congregational 13 Midos, he may finish the 13 Midos even after the congregation has finished, as this is also considered as being said with the congregation”, meaning that as long as the congregation is still saying Vidui he may say the 13 Midos, because it is a part of Vidui. C.      According to this, it is the same law with Selichos – as long as the congregation is still saying Vidui he may say the 13 Midos, but not after they finished. D.      This is not the opinion of the Leket HaKemach HaChadash (Section 4, P. 379, in the name of the Meorei Or) who says that as long as there are ten people together, even if they are not praying, he may say the 13 Midos alone. E.       It seems that the reason the Rebbe did not skip to saying the 13 Midos with the congregation while they were saying it, is because of the opinions that one should not skip prayers. Of course, we cannot say that the opinion of the Torah Lishma is the initial course of action to take. (see Halichos Olam section A, P.341)