They did have to pay shipping, I'm not sure about both ways though.
To my knowledge we have covered SH both ways on the majority of drivers that had the surround adhesion issue; pretty much all of them after a certain point as I issued a memo to the RMA department to send call tags when a customer supplied photos of this specific problem once we discovered it was a more broad issue. Some early returns may have been customer paid SH before it was really known -- if someone you know was in that situation have them let me know about it so I can give them some credit.
Customers were also given the option to DIY fix it if they were comfortable (we would still warranty it if that didn't work) -- which many did. In the majority of cases we also built entirely new drivers for the customers that sent their driver here rather than repairing what they sent to ensure that no release agent may have remained on the frame or surround.
That being said -- creating a whole new platform can involve some bugs. This particular bug was a bit of a surprise as the prototype parts were all fine -- production parts had a mold release agent applied to speed up manufacturing of the surrounds (we were not informed of this) and this caused the adhesive not to bond correctly. The same adhesives we had been using already for 5 years that had always worked and still do work on all other surrounds that we use.
Either way -- that has all been worked out to about 99.5% effectiveness through prep work & different adhesive when built here & prep work + bolt-on clips when build @ the factory. There have been some struggles along the way to finding an ideal solution but it's good to go at this point. To gain that final 0.5% effectiveness I went as far as tooling an entirely new Mega-Roll surround that is launching this year... in all four cones sizes (10, 12, 15, & 18).
As soon as we discovered it was a widespread issue on the early production units I pulled 100% of all factory Z v.4 inventory from the effected run and put it in our "QC Fail Yard Sale" so customers wouldn't get them as new woofers even with a small % chance of having an issue. The majority of the units sold through the Yard Sale have not exhibited the problem -- but some have -- so I'm glad I pulled them.
Typical RMA procedure is such that the customer ships to us at their cost so we can evaluate it -- as we do not know if they blew it up due to abuse until it arrives in most cases. If we can get sufficient evidence of a real defect before it is shipped here we'll typically issue a call tag to the customer as long as we can be certain of that before it is sent to us -- such as anyone who may still have an affected X or Z v.4 out there.