I was first in my class in hairsprings and have saved many considered "gone" but that one is GONE, and I'm the biggest optimist you'll meet. Even the best old dude from the Vallee de Joux would not even consider it.
I lost the driver cannon pinion in my clone 7750. I ordered a Swiss one, before I read that a Swiss one wouldn't work on a Chinese clone. I could not find out why until I received it. So just to let everyone know why it won't work is, the hole is to big on the Swiss one. The gear meshes perfectly though. So if the hole was right size it would work. If anyone knows where to get one for a Chinese clone, please let me know.
The height adjustment on all double roller rests is iffy at best. Files are like dogs, they might bite end off a sausage or wolf the whole thing down.
With a double roller rest, if it isn't perfectly parallel to the lathe bed you have a tapered square. If it isn't perfectly adjusted for height you have an oversize or undersize square.
With a single roller it's easy. You turn the diameter for the square to the diameter for the winding pinion. You turn the diameter for the front pivot to the square section of the winding square. You don't turn to the length of the winding pinion- just the square. Single roller rest, file until you just hit the pivot diameter. Index, repeat 4x. Now finish the pivot and the rest of the stem. With a single roller you can flip the rest at any time and measure what you're doing if you mistrust the pivot as guide. With a microscope you also see if you are tapering (possible with either single or double roller- there's no panacea) and correct. Your eyes are incredibly accurate for spotting tapers.
I usually cut the thread first, chuck on that and do the rest. Harden, temper, deblue with a bristle brush and white (steel) paste in the lathe holding the stem in a pinvice then clean up the thread and detent slot, burnish the pivot and large diameter that rides the plate/bridge. The brush usually cleans up the file marks on the square plenty. You want a 6 or 8 cut file for that. 8 best for the finish strokes.