Hello T42, welcome to the forum.
I know what you mean about the shower head sliding down. I have, I think, solved that problem. I took the whole thing apart and did a little modification to the holding mechanism. It is better now, but I don't know about the long run. If need be I will go to ver.2.01.
You will need to remove the lower arm cover by pulling straight out. Then unscrew the arm from the wall. The rod will then slide out of the top arm and you can lay the rod on a table to work on it. Push the release button on the shower head holder and slide it off. There is a small rubber "brake" pad in there that uses friction to hold the holder in place on the rod. Pry that out and put some sort of shim under it and then re-assemble every thing.
Attached are a few pics of what I did.
Peace
Dave