Some time ago I posted on why one should say over something in the name of whom he heard it from... ואמר ר"א אמר רבי חנינא כל האומר דבר בשם אומרו מביא גאולה לעולם שנאמר ותאמר אסתר למלך בשם מרדכי (Megillah 15A)
Now that I have had some more time to investigate this a little more carefully, I present the following.
Machzor Vitri: One should not be “Toleh” his Rebbe’s words as his own. Esther saying over the plot in the name of Mordechai started a chain of events which eventually resulted in the Geulah since Achashverosh then asked “What was done for Mordechai?”.
Derech Chaim: If a person is not even careful to say over who said something, you can be pretty certain that he is not careful to say over the saying correctly either.
Ruach Chaim: One is able to answer many questions by using the method “Leshitaso”…
Tiferes Yisrael: Of course one may not steal…but saying over in the Rebbe's name causes the Rebbe’s name to be mentioned for a Brocha…
It seems that many of the Meforshim learn that one should not steal. However, it is not really "stealing", as there is no tangible gain. That is precisely why this Memra is presented in Avos, which deals with Ethics.
The final comment is from the Medrash Shmuel. He says that "If someone steals someone else’s Torah, it prevents him from creating his own."
How Interesting! He is saying that less Torah will be learned if one can go and steal someone else's. But if I honor this saying and I need to say a Dvar Torah, I will then be forced to create my own. What a keen insight into plagiarism.
As the saying goes, "copying from one person is plagiarism, but copying from many is research"
I suppose the difference might be that even if you do copy, to copy from one person takes little effort, but copying from many sometimes takes years!