As far as I was able to ascertain, N54 135i SSK has been discontinued for a couple years; N55 135i SSK was never made.
There are several viable alternatives, from Dinan to UUC to different BMW SSK levers, but each may require some work. Is yours N54 or N55?
Posts 16, 44, and 97 on this thread provide some part numbers.
There's another SSK thread on here I didn't see you post in which gives additional detail:
http://www.1addicts.com/forums/showt...=414760&page=3
Good luck!
It really feels awesome once you find the right short-shifter for you.
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2012 E88 M-Sport 135i DSB Metallic
ER CP, ZHP Knob, E60 SSK Lever, E92 M3 FSB, RSFB inserts, Koni Sport, Eibach Pro, UCP, MPSS, AP axle-back, MHD Stage1+ 91
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