I figured out a way to mount a 120mm Fan at printer's motherboard,
to replace the very Loud 40mm fan, which I call Screamer !
It hangs directly below the Mobo and blows directly on it,
unlike the 40mm that mounts at one end of board.

Since 40mm fan is 24volt and I wanted to use a 12volt fan I had already,
I connected it to an external 12v power-supply, that I also already had.
That also gets some load off the printer's power-supply.

The 120 fan is only 15mm thick but seems to move almost as much air as a 25mm thick size.

Only problem is that it's So Much Quieter,
it's going to take some Time for me to get accustomed to 'No Screaming'