Help identifying please

It's difficult to identify what you have while it's still installed, but I believe we do sell the individual components of this assembly. See our 15-180 pivot shoe, 15-186 detent clip, 15-182 bushing, and Series 190 spring.

If there's no stamp on the spring, then the only other way to calculate its calibration is to weigh the sash on a scale. Tell me what that weight is and I'll tell you what option you need. Please provide the weight as precisely as you can manage, down to the ounce.