The other thing that causes a bike to want to turn in one direction but not so much in the other is a headset that's not quite right. The headset may be a bit tight and this may be affecting at one point on the bearing before others (this would be in the direction that the fork doesn't want to turn). Disassembling, cleaning, lubricating and reassembling the headset sometimes helps.
Or it could be a headset seating issue - if the headset isn't quite straight in the headtube, it will be tight at one point, which would cause the fork to not turn so readily in that direction. If this is the issue, a headset press would be needed for refitting the headset. The next level for that would be removal of headset and facing the ends of the headtube (which is probably a bike shop job unless you are Rogerzilla).