Is this the 15-177?

That's not our 15-177. I think a better match would be the 15-175.

As for replacement, we have a couple of videos that you may find helpful. I will link them below.

I would first try spraying WD-40 on the entire pivot to see if that loosens it. If not, go to the top and carefully unscrew the coil spring. Be very careful, though; use locking pliers on the coil spring to hold it firmly in place since it is under tension. If you aren't careful it will shoot out of your grip and you could damage the window or even hurt yourself. Make sure to wear gloves and goggles. 

Once you have a grip on the coil spring, try pulling up on the pivot shoe. See if that gets it out of position.