My experience.
After 27 000 km, dumpers are still happy. Some wears are there, but it is not problem yet. I am convinced that inner tube with silicone works.
Once yearly I am replacing pieces of rubber and apply silicone (because water is entering into hub over time and silicone is easily soluble).
Be carefully to not over lube (it happened to me, too).
However, good post from DirkZ and always be careful during the first ride, for any case.
Petre