Most of the time the screws holding the two sash halves together come out easily or after an application of penetrating oil and using gentle force. Sometimes though they break off, as can be seen here just left of center. To get the remaining stud out is somewhat of a challenge but it can be done by heating it with Mapp Gas until cherry red (watch out to not heat up the aluminum too much!) and then using locking pliers to gently rotate it out. If that doesn't help, or when the screw broke off flush with the screw hole, I've had good results using a carbide cutter in a Dremel Motor tool to carefully grind it out. Then an appropriately sized tap is used to re-tap the thread. I've been able to save several screw holes this way. On this side of the sash I also clean both flanges, especially the one visible at the top where the window gasket will sit against.