Je vais juste vous surprendre car je suis français.
JI'll just surprise you because I am French .
I understood the problem of the left fan. In fact the problem is with the design at Apple. The fan housing is too narrow vertically a few tenths of millimeters. This is why so many problems . The left fans deteriorate very quickly.
The solution is very simple. Buy a new fan in China, it is the cheapest and level it's very fast delivery . Warning it comes fan already used but in good condition.
The thing to do is to over- raise the fan does not rub and deteriorating. To do so just buy a zinc washer 3 mm diameter available from my local hardware store ( € 3 for 70 pieces ) and place it under the black screw fully right and top right . The over- elevation leads to no longer have friction effect.
Thats ALL !!!