Ah, a firm headquartered in España -- or on the chilly Baltic perhaps? You weren't the first to fall for the lure of those cheaper prices. I had wondered why you had to purchase your hoses separately and piecemeal together a new regulator set.
Sadly, your experience reflects something else that has been lost by many if not most dive shops nowadays. The place where I once worked tested every regulator that was sold. Since I was lowest on the totem back then, that often fell to me. We'd check for leaks at high pressure and let the regulator sit; verify a stable IP and cracking pressure; and jot those baseline specs for any future repairs or adjustments. A copy of the results would also go with the customer.
When I inquired of a local dive shop, whether that practice was still done, the replay was, "Where's the time?" -- the clerk, all the while, playing "Call of Duty" behind the counter. Some of those defunct shops years ago, would probably be seen as playing fast and loose with any number of things (taking wide-eyed OW students below 20 meters immediately springs to mind), especially by the pedants on this site; but the customer service and equipment support today is sorely lacking . . .
Wow, you do know your usual suspects! Espana hoses and Baltic reg it is
I did fall for the lure of cheaper prices, but after consideration of the following facts: the dealer is an approved Poseidon dealer, purchasing overseas does not appear to violate Poseidon policy or void warranty (contrary to Apeks, Scubapro or most other brands), the price difference vs US retailers is quite massive, and no local shop to me sells Poseidon regs. So my choice was either purchase online in the USA and pay margins for both a distributor and retailer not local to me, or purchase online in Europe and pay a single margin to an approved dealer. Agreed, I rolled the dice, but on something where my perception of Poseidon reliability indicated a very low chance of problems (obviously I was wrong there, but your report of never having heard of such a failure together with your apparent level of experience with Poseidon regs seems to indicate that I must have somehow been VERY unlucky here). Perhaps this is a lesson for the future, or perhaps not, and both the dealer and Poseidon will respond adequately and provide satisfactory resolution. We will see I guess.
As far as assembling the regulator with parts from different sources, I only did this because I wanted specific hose lengths that a fully stock assembled Poseidon reg set cannot provide, plus the fact that I had a gauge to test the set myself once assembled (fortunately!). But I do concede that I really didn't envision having those issues, obviously...