The left fan was noisy. In the past, I was successful in oiling them to quiet them. However, this time that didn't work. I took the laptop apart and cleaned the fan and tried to oil it. However, I was reluctant to try to take the fan itself apart.
The repair went smoothly. This was my third time inside the machine (once to add/replace memory, once to clean and oil the original fan). There isn't anything really exciting to report. I dropped a screw but I always do that at least once per project. I was able to find it so no missing screws.
This repair involves tiny screws. It's really easy to over torque them and strip the threads. Don't do it. The three holding the fan are just finger tight.
I bought my fan through iFixit. First, I wanted to make sure I was buying the correct fan. iFixit helped me with that. Second, they told me the Apple part number for the fan which allowed me to shop around. However, it's almost impossible to tell if a fan sold as "new" is really new or not. I ended up buying a new fan from iFixit. Yes, I paid more but the fan I received looks new and runs flawlessly. I'm willing to pay a bit extra for parts from a company which A) lets me see a guide for free and B) doesn't hide the manufacturer's part number.