Hello! You can replace just the broken parts in most cases, but in the case of the coil spring if you replace one then you ought to replace them all. You never want to mix old and new springs together since these lose tension over the years from constant use. In other words, even if the new spring is rated to hold the same weight as the old springs, it will still be stronger, given that it's brand new. That will lead to an uneven operation and, potentially, early failure.
With that in mind, your spring would be a match for either the 1/2" Series 160 or the 3/8" Series 165. You'll have to measure the original to verify the better match.
Concerning the pivot bar, you can just replace the broken one and be fine reusing the other side. No harm in that whatsoever. my recommendation would be the 26-378, but you should make sure our dimensions line up before you buy anything, just to be safe.
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