hey guys/girls. i just bought a 2010 wrx limited. no nav option on the vehicle, but it comes stock with the 10 speaker stereo and sirius. i found a used nav unit from a 2009 sti, wondering if anyone knows if this used unit will work in my 2010. does the antenna on my vehicle already have the nav antenna built into it? please let me know, i dont want an am unit that will attract attention but i want an in-dash nav, and this seems to be the best option