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There have been several threads on this problem. Try a search. My memory is that a plastic part on the seat mechanism wears out. You can fix it, but it looked to be quite a job to me. I'd use my warantee and get GM to fix it. If you don't use the "Easy Entry" function, you wear the seat mechanism less. I seem to remember that the part is stressed when the seat is all the way back, but not at other times. Poor design, I'd say.
The only fix I have seen is not an easy task.
I would take it in and have it fixed under warranty. They will probabaly replace the whole seat mech which should last just as long as your first one did. Then you can attempt the "rocking seat fix" yourself later on down the road after the warranty is up.
It can probably be fixed under warranty, although there is a VIN breakout involved, iirc. I suspect that putting the seat too far rearward, either via easy out or 'manually,' is one of the causes due to the seat back lifting the seat up as was described above.