Earlier this year I bought a NEW FasTrack 22.5 degree crossover from a well regarded forum sponsor located on the Atlantic Coast. The box appeared to be brand new with no signs of damage or excessive moisture. About half of the crossover's rails' surfaces were rusted. Another good portion of the rails had black spots on them (not the plastic). This appeared (my speculation) to be due to a factory electro-plating deficiency, perhaps combined with exposure to a humid salt air environment. Fortunately the seller happily offered to exchange the item and he even checked the replacement before sending it.
There are many things that need to go just right for the zinc plating process to work as intended, and even when it does, the plating will only protect from excessive moisture and water for a limited time before the sacrificial zinc coating is penetrated and oxidation begins to form on the base metal. My understanding is that initially, this oxidation can sometimes appear as black spots under the plating, prior to becoming the more familiar brown rust.
For anyone interested, here is a link to an expert discussion forum on how this process works and what can go wrong: Black spots in zinc plating
