Up to you. I always replace the rope, spring, pawl parts and o-ring.
BRP has the drop recoil assembly for your 2012 skidoo mxz TNT 600 adrenaline:
3aRewind Starter assembly Includes 3a to 12, [+] 415129800 $143.99 (sure is a bit spendy but it's a drop-in and I have a few pals that keep one with them in their parts pack. I don't as recoil maintenance is something I do every few years or at the onset of an issue or indication).
I keep a roll of recoil rope in the parts pack but the PN is listed below.
If rebuilding the recoil I would order the following (I always use new spring and pawl parts when in a recoil, had a few too many issues that had be go back to the recoil):
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