I finally got the bottle added. My 2012 GT/CS has 18k miles on it when I bought it and is sitting at 31k now. I have no idea if the PO did anything with the tranny fluid and I haven't. I went to add the XL-18 with just the front on ramps and when I removed the fill plug fluid started dumping. So I grabbed a quart of QDC from the dealer and made sure the car was leveled out on jacks the second attempt. I used a funnel and tubbing from the engine bay. Added the XL-18 and replaced the QDC that had spilled. I can definitely say shifting is much smoother both cold and hot. A lot of the notchiness I experienced while depressing the clutch and re-engaging the tranny is now gone. I also had a slamming feeling coming from the tranny/DS when under-driving sixth (cruising at 45, releasing the gas, and re-applying) that is all but gone.
I'm still debating switching to Redlines MTL or RP's Synchromax to see if there's any additional improvement using a higher quality fluid vice the QDC/additive mix.
Arrest Me Red 2011 GT Premium
Six-pot Brembo upgrade; GT500 rear brake upgrade; Whiteline adjustable front and rear sway bars; Whiteline adjustable panhard bar; BMR rear LCAs and relocation brackets; Eibach Pro springs; Koni STR.T struts and shocks; Eibach cam bolts; Legato axle-backs; Forgestar Matte Black CF5s - 19x9/19x11; Michelin Pilot Sport A/S 3+