Thanks for the guide. My 4-year old A1521 gave me a flash warning light. I fired up the utility app and it said the device was overheating. I put my ear against it and couldn’t hear any noise. I opened it up as shown here, removed the outer casing and powered it up, confirming the cooling fan was not spinning. I found quite a bit of resistance when I turned the fan by my finger. I had some 0W-40 fully synthetic motor oil laying around. I opened the fan up just by pulling the fan blade unit up and lubricated the shaft with the motor oil. And it worked out beautifully. The fan spins quietly and I get my green light back.
I should say the most tricky part was the step 1. I used a dinner table knife to open the base. Later in the process I did break a fan shroud clip. But the fan was hold tightly together with the screws in the end so it didn’t do any actual damage. It wasn’t a particular hot day, but without the fan the device did become warm and the internet speed was noticeably slowed down.