My local lumberyard called their paint supplier and they said if the paint has not completely faded from my factory baked steel siding that I do not need to prime, just paint. My common sense is telling me I must prime even if it's over the old paint. Does this make sense to anyone? I can see their point of view- why prime over paint? The paint is faded significantly on one side of the house (so of course I would prime that without a doubt) but the rest is fully intact. I did already scrub the house with TSP so it's ready to go.