Answers from R. Aron Leib Shteinman & R.Chaim Kaniyevski shlita

Gemoro  (Shabbos 55b)   "Whoever says Reuvain sinned, is only mistaken. It says in the Pasuk  ויהיו בני יעקב שנים עשר   ,

all were equal ."

How does the Gemoro know that Reuvain didn’t sin?  Maybe he sinned and did Teshuva and therefore he is equal to the rest of the שבטים ?

R. A.L. Shteinman shlita answered

The Pasuk  ויהיו בני יעקב שנים עשר is written immediately after

The Maaseh of  וישכב את בלהה Reuvain didn’t do Teshuva only

after  the Maaseh of Yehuda and Tamar ,  while the brothers were

selling Yosef to the Yishmaeilim. He was equal to the brothers before

doing Teshuva because he never sinned.

R.Ch. Kaniyevski shlita answered

Had Reuvain sinned and done Teshuva, he would not have been

equal to the brothers. He would have been greater than them.

במקום שבעלי תשובה עומדים אין צדיקים גמורים עומדים