Both left and right fans were very noisy and needed replacing, as previous repairs had only temporarily solved the problem. I ordered both a left and right replacement fan from iFixit.
The repair was straightforward
If you need to replace the left fan on this model (MacBook a1150) compare the screw tab to the original fan make sure it is the same thickness as the original. The tab in question is one closest to the mouth opening of the fan. If it is not, you can swap the housings like I did.