"Only Test 3 gives a slightly noisy result on two encoders during the first few revolutions, then after spinning them once or twice, they remain stable at maximum/minimum." - Mr_Dham
Thanks for testing yours!
"I've always wondered about contact cleaners. They can solve potentiometer noise problems temporarily, but don't they move the problem elsewhere? I don't know..."
That's always been my feeling too, but the reviewers seem pretty happy with that formulation.