In the meanwhile we sell much more reliable covers for the Doser.
We now use a new material which ran through a long-term test to achieve now extremely robust caps.
If you buy them at our store, it's sure that you get covers made from the new material: https://store.aquariumcomputer.com/e...nance-set.html

If you want to buy them elsewhere you can identify them following this instruction:
How to identify new blue dosing pump head caps.pdf