...made a mess under the sink. Looks like it is pitted on the sides, a steady stream passess thru when turning the water on. Has anyone ever gone through this, have the unit basically rust out?

 

Yes, they will basically rot. Most of the cases are made from cast aluminum, which will corrode over the years. Go ahead and drop $125.00 and get a new one. Remember to turn off the power before you work on it. Easy replacement.