Beethovens op 31 nr 3. Scherzo Vivace

[ignaceii]

For some time I wonder how I can get my left hand trained to get the bars 50 to 55 (and returning later) properly played. The bars are mixtures of fourths, fifths, and thirds, with the lowest note of the third equivalent to the upper note of the fourths and fifths (I hope I explain this well).
The tricky, nasty thing is repeatedly getting the common note firmly played. I tend to loose it when I play it the third, or vice versa.

This "problem" also occurs in the slow movement of the op 31 nr 1. The same there, but slower of course.

Starting slow, ok. But at tempo it is difficult. Perhaps there are ways of having preparing exercises to start with, or playing pieces of the chords repeatedly. Suggestions for fingering (see the imslp site for an example). I don't know.

If anyone recognizes my issue, any advise is very welcome.