Great, Rosco had the missing STi answer.
Unless you have a traction problem a front LSD might not be much use. A LSD will try and turn the front wheels at the same or a simular speed, this is good in a straight line, but when cornering it will increase the Subie understeer.
When hammering it around a corner what would help would be a bit of light brake pressure on the inside front wheel to try and slow it a bit and speed up the outside front wheel. This would improve the handling more than a front LSD. Unfortunately not an option on the older Subies. Maybe the new ones have it along with all the other electronic aids.
Didn't get specific with the diff oils as if I write too much or take too long writing it, it doesn't post. Just doing this to get my posts up so I can access other areas.