Good luck! It's a major P.I.T.A...I'd rather change the track out on my XP than try another lens change on the Sinister goggles.
I bought a pair of the polarized lenses for $40+ dollars...they didn't fit worth a chit in my 08' Sinisters (website claims the polarized fits both 08' and 09' models)! Took me at least an hour of pushing, poking, and prodding...ended up breaking the lens at the vent area in the top, trying to get the top of the frame over the lens. The inner lens wouldn't fit the frame of the goggle so I had to trim it down with some lexan scissors. It fits in the frame now but the broken vent area lets in too much wind. You have to start at the nose then work your way around to the top. I would definitely make a few practice runs with your old lens before trying it with the big $$ lens!
I sent an e-mail to "509" to see if I could return the lens and replace it at some sort of discount...anything would have been appreciated. I even asked if I could purchase a new set of goggles with the polarized lens installed. So far I have yet to receive any sort of response...been four weeks now. Great customer service there!!
I will say that the brown polarized lens offers great contrast in any condition...but I'll buy an overpriced pair of Oakley's before I purchase from 509 again.
Cory