I have just bought a 4.5 year old ‘360 – excellent boat and when I did a factory tour when looking to buy a new one, the factory told me that all the fittings were bronze as standard. Good I thought, except that upon inspection of the through hulls and fitting all were not Bronze nor DZR, and the heads outlet especially were very corroded (I found out that this has been replaced once already). Nothing had yet failed but I didn’t want these when in the water – like you! They were standard “brass” plumbing as far as I could tell from an unknown source. As i wanted to start from fresh with something that was genuinely solid, I have just replaced all of them below the waterline; not expensive as the cost is mostly in the labour. plastics are too tight to fit in most places as the fittings are much bigger, so I replaced them with Bronze where possible and DZR where not, which is a good long lasting combination. It appears that the factory genuinely get confused between what we call bronze and what is actually brass i.e. it has levels of Zinc even if it does have additions of Arsenic to assist in DZR state.
Upon enquiry I found out that most suppliers of production yachts also don’t fit good bronze parts which I would think should be the norm, or even can be guaranteed to fit DZR in all cases. they basically go for the lowest production cost, which can remain in good service for a number of years (at least past the 2/5 year hull warranty) which mostly they would do. Dufour is not unusual in trying to make a good balance between the best profit margin and the best attractive sales price.
Like most things you just need to look at what you have, assess the risks and improve the product to your satisfaction as you go along. you did the right thing IMHO for a comparatively low cost and now have “peace of mind” …..