We repaired a bunch of these for barges on the Fraser River here in BC. What we found is that the units were corroding and the upper circuit board was shot but the rest of the unit was salvageable. We simply designed and had made replacement circuit boards that the LEDs mount to. We also have switches and daylight sensing circuits.
If you've got a box of these that have failed send them in, we can rebuild them for a fraction of the cost of new.