I replaced the Wema level sensor sending units in both my fresh water and waste holding tanks about 18 months ago. The waste indicator stopped functioning again recently, so I removed it. A hard scale deposit, like salt or minerals, covered the stainless steel cover, float, and slide tube. After cleaning it all up, I checked the unit and it indicated properly. The float just wouldn't slide up and down due to the scale.I thought about greasing the whole thing to help slow down the growth of the scale, but didn't as I wasn't sure how that would affect the unit's operation.Is there a "preventive maintenance" procedure or tank additive to help with this?