Mine also lasted only 4 months before the major imbalance. Hopefully this isn't the lifespan of them. I heard somewhere that gold pin tubes do die a lot sooner then non gold pin tubes. Not sure what the reasoning was but to me 4 months just won't do for $99 tubes. IMHO at that price they should be guaranteed for at least a year as the insurance policy was definitely paid for.
I remember reading on some Russian site that these tubes were notoriously difficult to make, and apparently the QC was very basic. As far as I know they are not being manufactured any more - if that's really the case then only a merchant could provide such guarantee. But many sellers advertise 5000 hours lifecycle so maybe that is something to call on.