I too am revisiting this sonata (last performed in 1982!). Yes this passage is very challenging -- it even slows Horowitz down a bit (see on YouTube)! Given the geometry of the required anatomical movements, this is not ammenable to weight-transfer or osscilations of the hand. This is straight finger work -- so to speak. However, it can be carefully dissected to reveal certain difficulties and simplicities. The way to play this is ... ready for it ... to have your hand ready-prepared! Keeping in mind that velocity/acceleration is inverse to mass, you MUST use the smallest finger gesture possible in performance. However you may use greater gestures in training (thereby making it more difficult). Also, note the different combinations of movement which can be isolated and worked individually: LH:
5252525252525252 (not so easy)
5313131353131313 (not so easy)
5,23,1,23,1,23,1,23,1,23,1,23,1,23,1,23 (not so difficult)
Now, add all kinds of repeating rhythms, and do all of the above with slowly increasing metronome work, trying to get above performance tempo.
Above all (IMO), you have to modulate the strength and force of the 4-bar group; it should not be equal throughout but crescendo and decrescendo, ending with as much relaxation as possible. In the second 4-bar group you have to (IMO) bring out the moving G-Ab-G part. Also, don't forget that this is supportive material and you need to draw our attention to the RH.
Good luck! Maybe others will offer some help too.
Eddy M. del Rio, MD
"A smattering will not do. They must know all the keys, major and minor, and they must literally 'know them backwards.'" - Josef Lhevinne