Chosen Solution
Need the fitting that goes from the rear of the seat support bar, sU-shaped and fits into the upright riser bar and slides up and down when the chair is opened and closed, also there is a space between the cross bars below the seat that open and close the chair, I dont know if there is a spacer missing or not.
You are going to have to identify the chair before you can get the correct parts. Go the the Mediline website and see if you can identify it. That failing, contact the company and send them some photos, they will know what parts to photograph to assist you. https://www.medline.com/jump/category/x/…