Our club bought the D40+ balls early this year and recently within the last two weeks got some more in.
I'm not putting them next to a light to compare the seam but from what I've seen, they play the same as before. If a ball breaks at our club it's 95% of the time because someone accidentally steps on a ball.
We know that ever since the introduction of the plastic ball they keep making the process better & better in how they play. Seems to be that if you took price out of the equation, people rave about the Nittaku ball pretty much because it plays most like the old celluloid ball with it's very thin seam. I'm not sure if the thinner seam makes a difference or not but if DHS is tweaking the ball trying to improve it more & more, I'm fine with that.
We've only been hitting with this new ball since this year so I don't know if or when a change might have happened but honestly I'm not all that worried about it. I'm just glad for our club's sake to finally have a ball that is 40+, plays great, is durable and doesn't cost us an arm & a leg.
On a side note, while it's good to know about this change in the seam, I suggest Fabian, if he has the time, take say 5 of his old balls to club and 1 new ball and have a hit wit his training partner. See if there is a discernible difference in him being able to tell which ball is which.