They still work, kinda. When I was examining the inside of the case, I accidently hit the fans and knocked off one blade each fan. The problem is that it now makes the whole PC shake slightly. I suppose I should buy some new ones. Does it really matter what kind I buy?
Just check the diameter, it's usually 80, 92 or 120 mm. Get the cheapest fan you can find with a dBA-level below 18.