Not to attempt to answer in Jacobs place, and correct me if i'm wrong, but the very early run of the ZV.4 with the mega roll surround did have an Issue with the glue. Not every woofer of course, but for the first batches the they did not assemble the subs in house. However, as soon as Sundown realized there was a recurrent issue for the Zv.4 series they resolved it by designing a better system for securing the mega roll surrounds. They also switched to assembling the ZV.4s in house, i believe.
I have always been extremely impressed Sundowns products. I have purchased and installed several woofers from various levels and every single one has out performed my expectations. I had a single instance where I was sent a 10" instead of 12" woofer, but as soon as I had the woofer in the mail they had the correct woofer on the way, with faster shipping.
So if you are on the fence about dealing with the company or getting a quality woofer, GO FOR IT, You will not regret it.