Hi Vladimir, and Happy New Year!
I replaced the valves and valve seats and the seals. The pump head was in good shape, so I didn't replace it. Mine is not the duo, only 24v motor D60.
The parts were purchased from Great Water in Maine. There are a ton of small parts in this pump. I spent quite a bit of time trying to find them elsewhere without success. Mark is the USA Dessalator rep at GreatWater and is very helpful. I'm sure you could find a cheaper source if you're willing to spend the time looking for it.
I would like to ask several questions about watermaker pamp work that you successfully completed.
Where did you buy parts? Parts from DESSALATOR are rather expencive. Some part can be purchased on Ebay.
Did you replace only seals? Did you replace also valves and plungers?
Did you consider replacing the pump head? It probubly cost as much as you spend for parts.
What did you do with the motor?
SM #345 "LIFE IS GOOD"