You have a pars fracture on one side and a dysplastic pars on the other side. The dysplastic pars has elongated from years of partial fracture and healing similar to the limb lengthening procedures (Ilizarof procedures) performed on children with limb deformities. This allows a mechanical connection with the facets and explains the degenerative changes of the facets.
The report notes; “Mild annual bulge without central canal narrowing. Mild bilateral neural foraminal narrowing”. This means that the disc has suffered an annular tear. This tear precludes “fixing” the pars fracture. Also, by definition, the elongated pars has allowed a slip of L5 on S1.
What do your X-rays note, especially the standing flexion/extension X-rays?
Have you had diagnostic injections? Epidurals, selective nerve root blocks or discograms (not facet blocks)? The results of these would be quite important to determine what your pain generators are.