Although rotary distributors seem to be an old technology, there are many still in use today. In many cases the plants with them want to keep them. We have made them out of hot dip galvanized steel, stainless steel and aluminum.
All of our units are of the top bearing type; this keeps the bearing far away from the water. We promote a type with no lower seals if your situation allows. This means that there is no seal to wear out and start leaking; this is usually the first thing that needs repair on a typical unit.
This is a photo of an all aluminum unit, shortly after installation.