Very sorry to hear you've had such a problem and the only thing I can think that could cause such an issue, is that you live in an area with some kind of unusually corrosive element in the air, as nothing corrodes without something in the surroundings to cause it.
Those components are one of the few that we don't actually make ourselves but as a consequence they are items that are sold by the 1,000s by a range of companies (including Goodridge) and as we've never had a problem with them before (even when in use), we've had no reason to think they were inadequate for the job.
FYI we manufacture all the components that we sell large quantities of but untill recently, conversions to US spec fitting (in this case 4AN) have not been in big enough demand to warrant making them ourselves. However, the demand has been progressively increasing and as a consequence we are just waiting for a batch of suitable fittings for this job to be finished in stainless steel.
When they are completed I'd be happy to send you replacements but that could be a few more weeks yet.