Loctite should not be used at all. The way the mechanism is made, you will kick your own ass if you do use loctite. When you push the stirrup down to unlock, you are moving a fork that engages what looks like a flathead screw. That wedge shape that the fork engages will guarantee periodic adjustments in the future. That piece that looks like a flathead screw has a locking nut that needs to be tightened well. After adjusting the stirrup and riser should have no play. There's a bit of a delicate balance that needs to be done at this point. A bit too tight and that blue bar that disengages the stirrup will be impossible to move. You want the mechanism tight enough that the blue bar does not want to move until you smack the stirrup down.
If you've done it right, you will push down on the blue bar, give the stirrup a smack and the stirrup will fall away. Make sure you use a metal lubricant on the shaft, on the wedge of the screw head and the shiny chrome like locking pin.