I was working on Randal's special ending, picking the red options as they came. But somehow ended up with the same endings. What kind of influence did you have with the various factions?
Sadly, I didn't keep the save and don't remember other than it was pretty high with the Mavvar. Maybe the faction reputation isn't the (only) problem though. Depending on your personality, certain dialogue choices won't show up. For example, if you are constantly polite, certain rude responses aren't shown, so maybe this is the issue? If you try to get Randal's special ending, you might want to act like your typical Mavvar fanboy, believing in the revolution, putting him on a pedestal and everything.
Word of caution: No matter your route, if you are going for the special ending and you reach the point where you can get intimate with your mentor, then you missed your chance and are set for a "normal" ending. You can't have both hanky-panky and the special endings.