It’s the repeated Cs and Ds etc. that cause the trouble. The first C should be played as the end of a slur (B natural - C) and the second C as if it was the begining of
another slur — but without the arm lift on the next note, because of the continuity of the passage. Similarly with the two Ds etc.
The given fingering is the most satisfactory. Changing fingers on the repeated notes makes it more difficult to control the tone and leads to a tight technique.