Do you make a leshev when it's raining?
Yes.
Oy
http://hebrewbooks.org/pdfpager.aspx?req=30510&st=&pgnum=317&hilite=317-321
A single non-chabad source (read rishonim) would be nice
I didn't research the Rishonim, but there are quite a few non-Chabad sources starting at the bottom of this page:http://hebrewbooks.org/pdfpager.aspx?req=30510&st=&pgnum=318
(Maybe) he meant non-Chassidish.
I wouldn't call that the norm. I can't imagine that most people "enjoy" eating soggy food while getting drenched.
ואדרבה מרוב שמחת מצוה אינו מרגיש בגשמים ואינו מצטער.. וכן נהגו הצדיקים והחסידים אשרי להם ואשרי חלקם עכ״ל בעצי עדן וכר. וישראל קדושים מחמירים על עצמם ואינם יוצאים מן הסוכה
The Brisker Rov used to sit with an umbrella (chol hamoed) [brought down in the green jacket succah sefer]
Whats the Mekor for that?Isn't it the same as sitting under a Shlock?
In case this is coming next, it's true that minhag Chabad is not to even drink water outside of the Sukkah on shmini atzeres (even if it's raining), but obviously we do not make a brocha.
It does not necessarily constitute an ohel mafsik and therefore one can avoid the tzar and be mischayev. (according to some even a shlak may not passel a succah)