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I had the same problem with my Porsche 928 S2 with the did not staying open. I am sorry I did not take pictures as I fixed the problem but there are other threads on here that tell you how to remove the door arrestor/strap.
Once you have removed the door arrestor then you need to dismantle it. Usually the problem is that the round metal bar on either side of the door strap long bar has worn and this has meant that the friction the round metal bars use to halt the door at various points along the metal bar has ceased.
What I did was to replace the round metal bar with a metal bolt of the same diameter and this fixed the problem.
When reinstalling the door arrestor make sure that you insert the door arrestor bar all the way into the holder before you start the screw it back to the door as it will be so tight after you have inserted the new round metal bars that you won't be able to do it by hand afterwords.