On the mast there is a funny bit of aluminium that prevents the sail guides from dropping out of the rails. Since the proper screw to keep it in are missing I had to jury-rig it a bit. Since I prefer not to lose the original I went out on a limb and decided to use a 3D printer shop to copy the piece. Since it is not load-bearing I’d thought that plastic could do the job. It works great!

(Addendum in July 2020: with the new sail and its guides, the copy is not good enough and the guides can flip out under stress such as when dropping the sail. The original had to go back in. Now I have to modify the copies for a better fit.)