By far my first choice is to make my own replacement, but in the past when I did this I had a couple of issues. One, the larger 120mm case fan doesnt fit flush against the heatsink, and ends up being very bulky, and I have to have the fan blow INTO the heatsink because its very inefficient trying to draw air OUT without any casing.
So Im looking at the 80mm or 60mm. Now, I think I could fit these (def 60mm) flush against the heatsink, but with a smaller fan I dont know if blowing IN will be enough cooling, so Im considering how to fabricate my own casing for it to optimize airflow. The first thing I thought of was aluminum foil, as I can mold it to the exact shape I want and it wont be affected by the heat. However, it is conductive! Is there any way around this? If Im careful and dont have it touch the main board, do you think it would be OK?
How did the stock fan die? Is it just not spinning? I take it it's something that taking the fan itself apart and re-oiling wouldn't fix?
Fitting an 80mm fan into where the original one was doesn't sound like it would work. The mounting looks like it's all wrong, and the fan blades wouldn't really work in that application. The stock fan is designed to whip air out, rather than down, which is what a normal fan blade is designed to do. You could always try it, tho. If the $3 fix doesn't work, then you could try the $30.
If you have to go the $70 fix, it'll be a less hacked together one, and I can guarantee you'll see lower temps. Might be worth it anyways.