So you're talking about measure 30-34, hm? Well, if you have probs, try it this way: Try to move your right wrist (sorta shake it left-right-left-right etc.). Then the 2nd finger around the c, hold it and reach an octave with 1 and 5 - do the wrist move again, until you feel comfortable. Then, while moving, try to close in with your thumb step by step, e.g. pressing g, a, b ,c and then the d with 3, using your thumb again with the first 32nc in measure 31.
Once you're comfortable with that shaking movement (I'm sorry, but I don't know how to express that any differently).
It's interesting you don't have difficulties with the part starting in measure 77, coz I thought of this movement as being more difficult since a legato isn't easy to produce there.
Let me know about the pieces you selected.
Regards, - and good luck!