[Lapkritis]

It's likely a combination of things like you say... you do have to wonder on a stud such as mine that has the epoxy coating intact how large the role of corrosion played. All available literature describes the primary purpose of the epoxy to be for thermal insulation yet it also creates a seal that would prevent contaminants or corrosives from being introduced to the surface of the stud unless physically compromised such as a sloppy assembly ... which even then would be unlikely as the coating is quite durable. The embrittlement and/or risers must have occurred during the manufacturing... I do think the flat 6 air cooled design is partially at cause here due to the incredibly high, relative frequency of fastener failure. Either that or a manufacturer pumped out a huge run of compromised fasteners and a few different labelers continued to push them out after knowing (or not) the goods were tainted. I'd like to believe retailers would pull such product from the market place but who's to say inventory is thoroughly managed after it has been through a few wholesalers... they might not even know their stock delivered last week is 20yrs old.