On another note, reading through the discussion thread, I'm not sure if you are using the fan correctly on the heatsink. It need to be blowing onto the heatsink, not sucking air away from it. And the flap on the wind barrier is to allow some of the air to blow "down" off the heatsink onto the print to help it cool off faster when its open for very small ABS prints or PLA prints, and close the flap to reduce cooling on the print for larger ABS print.
I went from totally unable to print a specific kind of PLA to 75% success rate just by reversing the stock fan, so it sucks air away from the heatsink. This is pretty logical because a) it stops warm air from the top of the case to be blown against the heat sink and b) blowing this even more heated air against the extruder housing. I think sucking hot air away is the way to go. This has one disadvantage, you loose the function of the latch, as it needs to be shut while printing like this, as we don't want hot air from the hotend being sucked upward, against the heat sink. So with this you loose the ability to blow air against the PLA while it's printing. I am aware of this but it doesn't really seem to make much difference on the print quality.
Then, as 75% is not enough, I decided to add 2 fans to cool the stepper motor. First I oriented them to suck air away, but this didn't make any noticable difference... which I still don't understand as it's the most logical thing to do. Then I reversed them, so they blow air onto the stepper. This has taken success rate with PLA to 99%. There are still some spools that have issues, but I think they are of bad quality, as the first spool Black PLA from this supplier printed flawlessly, and the second spool I received a few weeks later is pure horror. Well the first 100 grams went ok, then it started to jam. I still don't have a solution for these spools, but as I have success with all others I don't really bother with them.
I print PLA mostly with a 10 degree drop (spools from 123inkt.nl), with closed bottom door, and opened top door. I get good prints, in an ambient temperature of around 18-20° C.