[Aredubjay]

My first binding problem was caused by mismatched tranny/rear end. Make sure someone hasn't replaced your tranny with a tranny from a Legacy. This, however is more than likely, not your problem.

Transfer clutches is the most common problem when binding occurs. Check your rear diff grease, and make sure it's full (though, I'll guess you've already checked this).

If yours is a recent installation, try making some (6-8) tight figure 8s. Sometimes the trans and rear diff need to "get to know each other better" after a fresh install.

You're right about the codes. You'll only get codes if an electrical component begins to go. Failing mechanical components do not show up in the self diagnosis feature. So, I'd suspect transfer clutch.

Try the LSD additive (oooo, flashback). Even if it doesn't "fix" the problem, it'll at least buy you some time to save the money for repairs.

Best o' luck.