The rails of the lumbar mechanism that carry the vertical adjustments shift forward and back. Unzip the seat cover (first undo the elastic hoops underneath the seat that secure the lower flap) and you’ll find that whole mechanism is loose when you apply some push/pull. I added a 6-7” long piece of thick pvc foam cut to fit between the rails and the plastic frame - where my fingers are. I’ve seen people use wine corks or whatever you have available as long as it is snug enough to eliminate the play. Hope this helps!
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