On our 76 450SL, the visors had collapsed foam and looked terrible. I cut the vinyl cover at the seam on top(the edge where the shaft is)and took the cover off. First rotate the end of the shaft 180deg-this rotates a lock pin inside and allows you to pull the shaft out. This allows you to remove the plastic gizzmo on the other end of the visor. In my case,I then wrapped new foam around the frame, glued with a spray contact cement and slid the cover back in place. I then lapped the cut edges over and glued. .You cannot see the glued edge when it's reinstalled. In your case, other repairs may be needed, but the R&R of the cover should be the same. Hope this helps.
Terry