but still- just shows that those cards were not manufactured properly if their solder joints are cracking.
no matter how well the card is manufactured in the first place, the joints will eventually fail. The joints are under quite a lot of stress when the card heats up and cools down, because of different coefficients of thermal expansion of the silicon/chip carrier/pcb-structure. Typical wear and tear so to speak. And since the failures follow some sort of weibull distribution, some joints will fail sooner rather than later, even if there wasn't anything obviously wrong with them in the first place...
anyways... it's likely the card wont last for long as mentioned already by others, there are plenty of other failure mechanisms going on in there, and even if this repair method fixes some, it will likely worsen some others.
But I'm glad to hear it worked again, even if it is only a temporary fix.