I had an issue with my new MACBook Pro 15: Mid 2009 within a day of ownership. The machine would not boot, corrupted hard drive. Apple replaced the hard drive, and a week later it did it again. Apple replaced the memory. A week later an Apple supervisor & I spoke and he agreed to replace everything in the machine. It worked OK from 2009 till a month ago.
3 months ago I added a second 500MB drive using an OWC Data Doubler. I used a SSD to boot from and put my USERS directory on the OWC Data Doubler drive. All this worked OK, but it did not give me the speed I thought it would given the bulk of the data was on a traditional hard drive, so I decided to purchase and Install two Momentus 750 GB drives. (Boot and all data on drive 1 and a backup of it on drive 2.)
Had issues with a corrupted boot disk while the drive was in the normal hard drive spot in the MACBook Pro. (It would work fine in the OWC Data Doubler position or externally.)
I examined the drive cable and noticed the little glue strips were not stuck to the body and appeared to be somewhat bent or crumpled (not flat). I am a very skilled repair type person and was very very careful with static discharge and handling this cable.
I took a chance and ordered the cable from IFIXIT, arrived sooner than expected and protected in great packaging. I installed it and everything worked better than it ever had since I bought the MACBook Pro.
In summery, I know this cable fixed my recent problem and I think it fixed the original issue I had with data corruption when I first purchased the machine. Perhaps this cable was not replaced by Apple as they said they did, after all cables never go bad, right?
Happy with IFIXIT
When troubleshooting always start with the easy stuff first.
Purchase parts from a known reliable vendor.
Be static discharge aware.