My wife's laptop was having very strange symptoms. The main filesystem sometimes logged as going read-only... Spotlight was broken, various programs didn't work and stalled out. I began finding very strange log messages that didn't make sense. It all led me to believe the disk was dying, so I took the opportunity to replace the slow HDD with a Crucial SSD -- except the symptoms showed up on the new drive. The Apple Store had the laptop for a day, but their diagnostics found no problems and they gave it back to me claiming it must be in the "user profile" (meaning her data). I reinstalled the system with a blank OS, none of her data (not even an iCloud login to sync data). And the problem persisted. Having ruled out both the disk and the data, I knew it must be the system. A bit of googling log messages led me to try the SATA cable next (and if that didn't work, the next step was to buy another laptop!)
It went well. This cable requires you to stick it to the case (part of the cable is like a sticker and you peel the backing off), and that took a bit of fooling with it. Also I bought the bracket-less variant of this part, so I had to take off the sleep indicator light and the IR sensor and reattach them to the new cable. I didn't want to deal with that, but the part with the bracket attached was not in stock, so I had no choice. There's a very small ribbon cable involved in that swap, which was a pain, but I got it after a couple of minutes. If it's in stock, buy the cable with the bracket already attached; it's only a $10 difference and is probably worth it. The rest of the repair was pretty straightforward
Slow and steady wins the race when you're dealing with delicate parts and these semi-rigid ribbon cables. Move slowly and think about what you're doing before you pick up the next tool. Also, always, always, ALWAYS look at the logs and google the odd messages there. Someone else out there has had the problem that you're having, and hopefully they wrote about it somewhere like a forum or a mail list, and you can benefit from their pain. If not, well, go write about your problem somewhere... the next guy will appreciate it.