I have had my DVs out many times , cleaned and oiled with carb oil like recommended.
My claim is that oil used is critical. My valves is sticky operation on.
I made a video that is in progress to be published , it shows how valve operates when applied vacuum to , how I serviced them and after how smooth they operate with new kind of oil , a thicker , much thicker type oil.
My valves needed a lot of vacuum before they started moving , and did not return properly always.
Now they start with much less vacuum applied and return properly.