A related recommendation (may be helpful to others in future searches).  Our bilge pump activation switch began to fail, staying on even after the cord pulled the switch down and into the off position.  This was gradual, at first fixed by simply cycling the switch but finally just staying on.  I ordered a replacement assembly from Amel. In the meantime as a stopgap measure I shot Corrosion-X into the switch (after removing the sump tube and switch so I could work with it on the dock holding it in different positions).  I collected a great deal of black residue in paper towels and continued sprays until I had no residue.  Replacement switch came a week later but switch was working just fine.  It has now been about 5 years.  I squirt Corrosion-X into the switch periodically, including the contacts. I would encourage anyone cleaning the tube to conduct the same procedure until the residue is clear.

Bob KAIMI SM2K 429 

Vice-President, Corrosion-X Consumer Advisory Council of North America
Director, Amel Institute of Low Technology