There is no reason for any type of fastener to rust or bleed discoloration unless it has come in contact with moisture from some source. Otherwise, all of the nails in our stick houses would be showing through. It would also take quite a while for that condition to develop. The only places on my ceilings that have ever yellowed was caused by roof leaks.
I would start looking for air conditioner ducts and discharge grills that were not properly taped at manufacture and are likely putting cold air into the roof area causing condensation. After that, water would travel along almost any surface through gravitational effect, stopping at the bottom which would be the roof material.
Also, if this were a common fastener problem, we would be seeing many more posts about it.
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2011 Outback 277RL
2013 F250 XLT Crew Cab 6.2L
Bitter Gun Owner
Bitter Clinger
Armed Infidel
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