My dive buddy just got a new D500 and Nauticam housing. After putting a new dome on it, he found it would not hold a vacuum. After many hours of puzzlement, he found a dog hair on the main, not port o-ring. Problem solved, and brand new camera saved. Dove once with a guy who had a Red Epic. His housing would not hold a vacuum, but he dove with it anyway because he had "insurance". Maybe, he just wanted cash or a new camera. The housing flooded almost immediately.
I have never had a flood or leak with my Nauticam vacuum system. Once, the vacuum was slowly lost, and I did not take it diving. That probably saved my camera.
I have a trip coming up as well, but my one working(so far) YS-D2 is not going. The problem is that Inon is no longer making the equivalent z-240. This should be a golden opportunity for Retra to break into the market, but they are not shipping yet. I decided to have my old Inon 240-zs refurbished. They are over 10 years old with more than 1000 trouble free dives on them. They have lost some power, which was the reason I am replacing them, but some power is better than none. Backscatter tells me they should work like new after the refurbishment.
What is your shutter speed? Strobes will not synch if it is too fast. Maybe, try it on another camera/housing if you can get access to one.
On the other hand, this is a very problematic strobe model. If you become certain the strobe is the issue, I suggest you aggressively seek to have it replaced, not sent off to Japan for 6 months to get repaired.