You don't need part #12,13 anymore. The Si and non Si models have the same part number for the mounting points for the bushings. The 8th gen they were different.
I would recommend buying new since the "used" price isn't much off with shipping factored in. Also, new bushings come with the new bar.
EDIT: @Pauly99to17
http://9thcivic.com/forum/threads/2-year-progress-rear-sway-bar-update.8172/
If he doesn't buy new he'll still need those parts.
22mm Progress RSB installed on my R18 (yes, I know the bar is upside down in the pictures):
22mm Progress RSB installed on a 2012 Si:
Notice how the 22mm bushing/holder fit perfectly on the Si mounting brackets whereas the R18 mounting bracket ends at the bottom of the bushing itself, which is why extra hardware is included with a new Progress RSB.
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